This paper proposes the architecture of collaborative working environment ACE, an agent-based collaboration environment. Users of the system can work in collaboration with others via message, which is managed by Message Management System (MMS) at the center of the system. To give collaboration assistance to users, ACE has three agents in MMS and a personal Desktop Agent for each user : Repository Agent collects messages between users, Address Match Agent gives suggestion of members' list for community organization, and Topic Management Agent logs communication session. Agents in the ACE speak Agent Communication Language to provide appropriate information for their users. A simple prototype of ACE system has been built and evaluated by a scenario of distributed ship maintenance, which requires collaboration of workers on land and at sea.