日本の通信エリア

日本 の数値が意味すること

重要な数値は2つあり、どの会社も引用するのはそのうち1つだけです。一般的な速度は74 Mbps。調子のいいときがどれくらいかを示す数字です。

読む価値があるのは10パーセンタイル、21 Mbpsのほうです。駅の上の基地局が混み合い、周りの全員が同じ電波につながっている、その日の下位1割のときの速度です。中央値が高くて下限が低い国は、本当に必要になるその瞬間まではみごとに動く国だということです。

ビデオ通話やテザリングが欠かせない旅なら、一般的な速度ではなく混雑時の数値を基準に計画してください。

日本で回線が混んだときに起きること

混雑は故障ではなく、火曜の夜です。問題は、そのときeSIMに何ができるかで、たいていの旅行用eSIMの答えは「何もできない」です。国ごとに卸契約が1つ、ネットワークが1つ、路上に立ったまま他社のeSIMをもう1枚買う以外に逃げ道がありません。

ここではOrbisloの通信はKDDI、SoftBankを通ります。いま乗っているネットワークが劣化したら、旅行の途中でも、お客様が頼まなくても別の回線へ移します。そのときに邪魔をするのではなく、あとからお知らせします。

日本の携帯キャリア

• NTT Docomo: NTT Docomo held 32.9 percent of Japan's mobile contracts at the end of March 2026 on the ministry's count, rising to 39.5 percent once lines it supplies wholesale to virtual operators are included, making it the largest of the four licensed networks.
• KDDI: The KDDI group held 26.2 percent of mobile contracts at the end of March 2026, or 31.4 percent including the lines it supplies to virtual operators.
• SoftBank: SoftBank held 18.7 percent of Japan's mobile contracts at the end of March 2026, or 24.6 percent including the lines it supplies to virtual operators, according to the communications ministry's quarterly figures.
• Rakuten Mobile: Rakuten Mobile held 3.6 percent of mobile contracts as a network operator at the end of March 2026. Virtual operators running on the other networks together held 18.5 percent.
• Rakuten Mobile, 700 MHz: In October 2023 the ministry approved Rakuten Mobile's plan to build base stations in the 770 to 773 MHz block. Rakuten was the only applicant for that 700 MHz band spectrum, which was assigned with conditions attached.

日本の旧世代ネットワーク

• KDDI and Okinawa Cellular switched off au's 3G service, CDMA 1X WIN, on 31 March 2022, after running it since November 2003. From 1 April 2022 au handsets that could not make VoLTE calls stopped working.
• SoftBank ended its 3G service on 15 April 2024, having postponed the January date after the Noto Peninsula earthquake. Customers living in Ishikawa Prefecture kept 3G inside that prefecture until 31 July 2024.
• NTT Docomo closed its FOMA 3G network and the i-mode service on 31 March 2026. Since then a phone that cannot make VoLTE calls, or has VoLTE switched off in its settings, cannot make voice calls on Docomo at all.

日本の5G

• In April 2019 Japan assigned its first 5G spectrum to four operators: NTT Docomo and KDDI with Okinawa Cellular received two 100 MHz blocks each between 3.6 and 4.6 GHz, SoftBank and Rakuten Mobile one each, and every operator also received a 400 MHz block between 27.0 and 29.5 GHz.
• In December 2024 the ministry approved SoftBank's plan for the 4.9 to 5.0 GHz band, the only application it received, adding a further 100 MHz of 5G spectrum to SoftBank's network.
• At the end of March 2025, 5G reached 98.4 percent of Japan's population when the four operators' coverage is combined, and between 88.4 and 99.9 percent in each prefecture. The government's target is 99 percent nationally and in every prefecture by March 2031.
• By the end of March 2026 Japan counted 126.32 million 5G contracts, up 12.7 percent in a year, against 108.85 million 4G contracts, so 5G lines now outnumber 4G ones.

日本のネットワークについて

• Since 1 April 2026 the four network operators run JAPAN Roaming: when a disaster or major outage knocks out one network, its customers can switch to another at up to 300 kbps, or in some cases make emergency calls only. The phone shows a network name such as JPN-ROAM D, K, S or R.
• JAPAN Roaming is switched on only for large scale disasters or major network failures, not for everyday or small outages. Smartphones from roughly the spring 2026 models onward are expected to support it, and some older models gain support through software updates.
• The January 2024 Noto Peninsula earthquake took up to 839 mobile base stations off air across the four networks, 799 of them in Ishikawa Prefecture, as power cuts and severed transmission lines spread. KDDI, SoftBank and Rakuten Mobile finished emergency restoration on 15 January and Docomo on 17 January, except where landslides blocked access.