| Areanet Co., Ltd | Shizuoka |
| Arigatobank, Inc. | Tokyo |
| Aristo Japan Co., Ltd | Tochigi |
| ARK Co., Ltd | Tokyo |
| ArkEdge Space, Inc. | |
| ARKRAY Co., Ltd | Kyoto |
| ARM Ltd | Tokyo |
| Armonicos Co., Ltd | Shizuoka |
| Arrow Electronics Japan Co., Ltd | Tokyo |
| Art-Labo | Fukuoka |
| Artas Software Corporation | Tokyo |
| Arteria Networks Corporation | Tokyo |
| ARTham Therapeutics | Tokyo |
| Arttech Co., Ltd | Fukuoka |
| AS-Accelerator | Saitama |
| Asahi Advertising Co., Ltd | Tokyo |
| Asahi Diamond Industrial Co., Ltd | Tokyo |
| Asahi Electronics Laboratory Co., Ltd | Osaka |
| Asahi Intelligence Services Co., Ltd | Tokyo |
| Asahi Media Lab Ventures | Tokyo |
| Asahi Tech Co., Ltd | Osaka |
| Asahigakuen | |
| Asahikawa City University | |
| Asahikawa Medical University | |
| AsahiNet | Tokyo |
| Asakurasoft Co., Ltd | Tokyo |
| Asama Software Corporation | Nagano |
| Asapnetwork Co., Ltd | Tokyo |
| Ascent Development Services | Tokyo |
| Ascent Robotics Co., Ltd | Tokyo |
| Ascentech Co., Ltd | Tokyo |
| Asco Japan Co., Ltd | Hyogo |
| Ash Multimedia Lab | Tokyo |
| Ashikaga Bank Ltd | |
| Ashiya University | |
| Asia Commerce Ltd | Tokyo |
| Asia Pacific Computer Emergency Response Team | Tokyo |
| Asia Pacific Networking Group | Hiroshima |
| Asial Corporation | Tokyo |
| Asian Productivity Organization | |
| AsiaQuest Co., Ltd | Tokyo |
| ASIOT Co., Ltd | Tokyo |
| ASJ | Tokyo |
| Ask Co., Ltd | Tokyo |
| ASKA Pharmaceutical Co., Ltd | Tokyo |
| Asobie Co., Ltd | Tokyo |
| ASOBIMO Co., Ltd | Tokyo |
| ASP i-do | Tokyo |
| Astellas Pharma Co., Ltd | Tokyo |
| Asteria Corporation | |