What a local exchange code is
A Japanese landline number is built from three blocks: the area code, the local exchange code, and the subscriber number. Area codes are set region by region in a public notice, so they tell you where a number belongs. The local exchange code that follows is assigned by the Ministry of Internal Affairs and Communications to each telecom carrier, and under Japan's numbering plan the code itself carries no geographic meaning. Reading this alongside how Japanese phone numbers are structured makes it easier to see which part of a number stands for what.
In 03-3456-XXXX, for example, 03 is Tokyo's area code, 3456 is the local exchange code, and XXXX is the subscriber number. Location comes from the first block. There is no published table that turns those four middle digits into an address.
How the digit count is decided
Local exchange codes run from one to four digits, and the length varies by region. The area code and the local exchange code are combined so that together, counting the leading zero, they always come to six digits. A short area code therefore leaves room for a long exchange code, while a long area code leaves room for only a short one.
- Tokyo (03): 2-digit area code + 4-digit exchange code
- Osaka (06): 2-digit area code + 4-digit exchange code
- Sapporo (011): 3-digit area code + 3-digit exchange code
- Hakodate (0138): 4-digit area code + 2-digit exchange code
- Areas with a 5-digit area code: 5-digit area code + 1-digit exchange code
The six-digit rule exists so that, together with the four-digit subscriber number, every landline number lands on ten digits. As the history of phone number length describes, digits were added step by step as the number of subscribers grew.
What a local exchange code can tell you
Location comes from the area code
Because the exchange code has no geographic meaning, you cannot narrow a number down to a ward or a neighborhood by reading the second block. The clue sits in the area code instead. Following the steps in the area code lookup guide is the reliable way to place a number.
Why it is also called an exchange office code
The alternative name comes from the analogue era, when blocks of numbers were used one switching office at a time, each office serving the lines wired to it. Numbers hosted on the same equipment can go down together if that equipment is damaged. Which numbers sit on which facility is not published, though, so a shared exchange code is no proof of shared equipment.
Why digit counts differ by region
Crowded areas run short of spare codes
In areas with many subscribers, such as Tokyo and Osaka, the supply of spare exchange codes is the binding constraint. Tokyo's 23 wards moved from three-digit to four-digit exchange codes in 1991, which greatly increased the number of available combinations. Disconnected numbers are also held for a period and then issued to another subscriber; as recycled phone numbers explains, calls meant for the previous holder can keep arriving.
Long area codes leave short exchange codes
Where the area code is long, only one or two digits of the six-digit budget are left for the exchange code. The four-digit subscriber number still covers the number of subscribers such an area has.
IP networks and switching equipment
Japan's landline network was moved onto IP networks in stages from January 2024, and the migration was finished by January 2025 (the move away from the PSTN). Subscribers kept their numbers through the switch, but a number after the migration does not map one to one onto a particular building or piece of switching equipment.
How to find the region behind a number
When you want to know where a number is from, work from the area code.
- Phone number databases: entering a number on a database such as this site, Denwa, shows the region that matches its area code along with the reports other people have left about that number
- Company and store pages: corporate profiles and store listings usually print the phone number and the address side by side
- Old directory listings: the printed Hello Page directory has been discontinued, though some of what it carried survives in other forms
- Directory assistance is closed: NTT East and NTT West ended their 104 directory assistance service on March 31, 2026, so there is no phone line left for asking which region a number belongs to
Keep in mind that a virtual phone number or a cloud PBX lets a business hold an area code that has nothing to do with where its office sits. A number starting with 03 is no proof of a Tokyo address.
Exchange codes, nuisance calls and scams
Nuisance and scam calls are often placed from blocks of numbers obtained together and then worked through one after another. Repeated suspicious calls that share an exchange code are a reason to suspect that one caller is cycling through a block. What the block cannot tell you is where that caller is, because the code carries no geographic meaning. When you turn to the reporting routes for phone scams, having the number and the date and time written down makes the situation easier to explain.
Where exchange codes stand after the IP migration
With the IP migration and the spread of cloud PBX systems, the exchange code works as a set of digits that identifies a number rather than as a pointer to a switching site. Even so, some people read a landline number with a local area code as a sign that a business keeps a settled contact point. As choosing a business phone number sets out, taking a local area code or going another route is a decision about how a business presents itself.