Prefixyr.com
Japan ☎️ Landline / Geographic

Area Code 423 – Kokubunji, Tokyo

The phone area code for Kokubunji, Tokyo is 423 (international format +81423). Browse local exchange codes (NXX) and carrier assignments below.

Current Local Time
17:45:12
Asia/Tokyo • UTC +09:00
Full Dialing Format
+81423
Population 129,242
👥
Admin Region Tokyo
🗺️
Elevation 78m
🏔️
GPS Coordinates 35.7022, 139.4756
📍

📍 Geographic Location of Kokubunji, Tokyo

Overview of Area Code 423

Area code 423 is a geographic numbering plan area within the Japanese telephone numbering plan, assigned to the city of Kokubunji and its surrounding areas in the western part of the Tokyo Metropolis. Under the ITU-T E.164 standard, the international dialing format for this region is +81 423 XXX XXX, where +81 is the country calling code for Japan, 423 is the national destination code (NDC), and the remaining seven digits constitute the subscriber number. Within Japan, the national trunk prefix 0 is used, so domestic callers dial 0423 XXX XXX.

Geographic Coverage and Administration

Kokubunji is a city located in the Musashino Terrace of western Tokyo, approximately 30 kilometers from the central wards of Tokyo. The area code 423 serves not only Kokubunji but also parts of neighboring cities such as Koganei, Kodaira, Tachikawa, and Fuchu, depending on the specific exchange boundaries. This region is primarily residential and commercial, with several universities and research institutions, including the National Institute of Informatics and the JAXA Chofu Aerospace Center, which are served by this numbering area.

Dialing Formats and Caller Instructions

For local callers within the same numbering plan area (i.e., dialing from another number with the same area code 423), it is possible to dial the seven-digit subscriber number without the area code in some cases, but for clarity and to avoid misdialing, it is recommended to always include the area code. For domestic callers from other areas in Japan, the correct dialing format is 0-423-XXX-XXX. For international callers, the format is +81-423-XXX-XXX (or 011-81-423-XXX-XXX when dialing from the United States).

Overlay and Numbering Considerations

Currently, there is no overlay plan for area code 423; it remains a standalone area code. However, as part of Japan's telecommunications numbering plan, the Ministry of Internal Affairs and Communications (MIC) periodically reviews numbering resources. Subscribers in this area are served by NTT East and various competitive local exchange carriers, and number portability is available for fixed-line services, allowing users to retain their numbers when switching providers.

Practical Examples

  • Local call (within 423): 0423-XXX-XXX
  • Domestic call from Tokyo (03): 0423-XXX-XXX
  • International call from the US: 011-81-423-XXX-XXX
  • International call from the UK: 00-81-423-XXX-XXX

Understanding the correct dialing format is essential for businesses and individuals communicating with this region, ensuring seamless connectivity in Japan's advanced telecommunications network.

❓ Frequently Asked Questions

What city does area code 423 in Japan cover?
Area code 423 covers Kokubunji and parts of neighboring cities in western Tokyo, including Koganei, Kodaira, Tachikawa, and Fuchu.
How do I call a number in area code 423 from abroad?
Dial your country's international access code (e.g., 011 from the US, 00 from most European countries), then Japan's country code 81, followed by 423 and the seven-digit subscriber number. For example, 011-81-423-XXX-XXX.
Do I need to dial the area code for local calls within 423?
In many cases, local calls within the same area code can be made by dialing just the seven-digit subscriber number. However, it is recommended to dial the full number including the area code (0423-XXX-XXX) to ensure proper routing, especially from mobile phones or VoIP services.
Is area code 423 a mobile or landline prefix?
Area code 423 is a geographic landline prefix assigned to fixed-line services in the Kokubunji area of Tokyo. Mobile numbers in Japan have their own prefixes, such as 090, 080, and 070.
Can I keep my landline number if I move within the 423 area?
Yes, as long as you move within the same geographic area served by area code 423, you can typically keep your existing landline number. If you move outside the area, you may need to change your number, unless number portability rules apply.