| ClinCloud Ltd | Tokyo |
| Clinical Network LLC | Tokyo |
| Clipla Co., Ltd | Tokyo |
| CLIPS | Niigata |
| Closip Co., Ltd | Tokyo |
| Cloud Ace Co., Ltd | Tokyo |
| Cloud CIRCUS Co., Ltd | Tokyo |
| CloudCore Co., Ltd | Tokyo |
| Cloudear Co., Ltd | Tokyo |
| Cloudpoint Co., Ltd | Tokyo |
| Cloudrop Co., Ltd | Tokyo |
| Clover Design Co., Ltd | Nagano |
| CLUE Co., Ltd | Tokyo |
| Cluster, Inc. | Tokyo |
| Clutch | Tokyo |
| CMAN Co., Ltd | Osaka |
| CMS Solution | Tokyo |
| Co-step Co., Ltd | Tokyo |
| Coastal Development Institute of Technology | |
| Cobnet Co., Ltd | Tokyo |
| Code Chrysalis | Tokyo |
| CodeCamp Co., Ltd | Tokyo |
| CodeComplete Group | Tokyo |
| Codegym Co., Ltd | Tokyo |
| Cogent Labs Co., Ltd | Tokyo |
| COGNANO Co., Ltd | Kyoto |
| Collaboration Plus Co., Ltd | Tokyo |
| COLOPL Next, Inc. | |
| Comcraft Corporation | Tokyo |
| Comitia | Tokyo |
| COMIX | Tokyo |
| Commerce Robotics Co., Ltd | Tokyo |
| Commufa | Tokyo |
| Communication S | Tokyo |
| Communications and Information Network Association of Japan | Tokyo |
| Communitio Corporation | Tokyo |
| ComnetSystem Corporation | Tokyo |
| Comnico, Inc. | |
| Compcare, Inc. | Niigata |
| CompleCure, Inc. | |
| Compliance Management Co., Ltd | Tokyo |
| Computec Engineering Ltd | Tokyo |
| Computer Aided Test Systems Co., Ltd | Akita |
| Computer Dynamics Co., Ltd | Tokyo |
| Computer Engineering & Consulting Ltd | Tokyo |
| Computer Engineering Co., Ltd | Fukuoka |
| Computer Entertainment Supplier's Association | Tokyo |
| Computer Institute of Japan | Tokyo |
| Computer Kyoiku Gakuin | Fukuoka |
| Computer System Service Co., Ltd | Chiba |