| ASTI Corporation | Shizuoka |
| ASTOM R&D | Saitama |
| Astrodesign, Inc. | Tokyo |
| Astroscale Holdings, Inc. | |
| Asuka Index Co., Ltd | Tokyo |
| Asukanet Co., Ltd | |
| Asuzac Co., Ltd | Nagano |
| Asware Co., Ltd | Tokyo |
| AT Partners Co., Ltd | Tokyo |
| AT System | Tokyo |
| At-Link | Tokyo |
| AtCoder Co., Ltd | Tokyo |
| Atelier Ishikawa Co., Ltd | Kanagawa |
| Atika Bank Ltd | |
| ATL Systems, Inc. | Tokyo |
| Atlan Corporation | Tokyo |
| Atlus Co., Ltd | Tokyo |
| Atmark Corporation | Tokyo |
| atmarkIT | Tokyo |
| Atom Co., Ltd | Tokyo |
| Atomitech Co., Ltd | Tokyo |
| Atonarp Co., Ltd | Tokyo |
| atP's Corporation | Tokyo |
| Atrea, Inc. | |
| Atsugi Isehara Cablenetwork, Inc. | Kanagawa |
| Attack System Co., Ltd | Tokyo |
| au Payment Corporation | Tokyo |
| Audio Note Co., Ltd | Tokyo |
| Autify, Inc. | Tokyo |
| Automatigo Co., Ltd | Tokyo |
| Autoprocessing Co., Ltd | Tokyo |
| Avaldata Corporation | Tokyo |
| Avalon Technologies Co., Ltd | Tokyo |
| AViC Co., Ltd | Tokyo |
| AWL Co., Ltd | Tokyo |
| AWS Co., Ltd | Toyama |
| Aww, Inc. | |
| Axcelead Drug Discovery Partners, Inc. | |
| Axell Corporation | Tokyo |
| Axelspace Corporation | Tokyo |
| Axis Co., Ltd | Tokyo |
| Ayumi Trust Holdings Co., Ltd | Tokyo |
| AZ Co., Ltd | Tochigi |
| Azbil SecurityFriday Co., Ltd | Kanagawa |
| Azden | Tokyo |
| b-mobile | Tokyo |
| B.U.G., Inc. | Tokyo |
| Baby Universe Co., Ltd | Kanagawa |
| Baidu Japan | Tokyo |
| Bancho Corporation | Tokyo |