Area Code 138 – Hakodate, Hokkaido

Geographic Coverage and Administrative Jurisdiction

Area code 138 is a geographic National Destination Code (NDC) assigned to the city of Hakodate and its surrounding municipalities in the southern part of Hokkaido, Japan. This region falls under the administrative jurisdiction of the Hokkaido Prefectural Government. The code covers Hakodate City proper, along with nearby towns such as Nanae, Shikabe, and Mori, which are part of the Oshima Subprefecture. As a geographic code, it is tied to the physical PSTN infrastructure of the area, though VoIP services may also use this code for virtual numbers.

Primary Cities and Coverage Area

The primary city served by area code 138 is Hakodate, a major port city known for its historical landmarks and tourism. The coverage area extends to the eastern part of the Oshima Peninsula, including the municipalities of Hokuto (formerly Ohno and Kamiiso) and the southern reaches of the Nanae township. The code does not cover all of Hokkaido; other regions use different area codes (e.g., Sapporo uses 11, Asahikawa uses 16).

Dialing Formats and Instructions

For local callers within the Hakodate area (i.e., when dialing from another number with the same area code), the national subscriber number is typically 6 digits, and the local format is 0-138-XXX-XXX (where the leading 0 is the trunk prefix). However, when dialing from outside the area but within Japan, callers must dial 0-138-XXX-XXX (including the trunk prefix 0). For international callers, the format is +81-138-XXX-XXX (dropping the leading 0).

Example: A local number in Hakodate might be 46-XXXX. To call this from Tokyo, you would dial 0-138-46-XXXX. From the United States, you would dial +81-138-46-XXXX.

Overlay and Numbering Plan Considerations

As of the latest ITU-T E.164 national numbering plan, area code 138 does not have an overlay code; it remains a standalone geographic code. The Japanese Ministry of Internal Affairs and Communications (MIC) has not introduced overlays in this region, so 10-digit dialing (including the trunk prefix) is mandatory for all calls to Hakodate from outside the local area. Within the local area, 6-digit dialing may still be permitted for local calls, but this is subject to carrier-specific routing.

Caller Instructions

For local callers within Hakodate: If you are calling a number within the same area code, you may dial the 6-digit subscriber number directly (e.g., 46-XXXX). However, to avoid confusion, it is recommended to always dial the full national number (0-138-46-XXXX) from mobile phones or VoIP services. For foreign callers, always use the international format +81 138 XXX XXX (without the leading zero). Ensure you have the correct country code (+81) and drop the trunk prefix 0 when dialing from abroad.