This paper proposes an architecture for realizing cooperative work by a multiple robots system. Cooperative work is regarded as being performed by a set of dynamic units called functional modules. A functional module is defined by nine objects, i.e., a data acquisition object, a data analysis object, an environmental information object, a communication object, a control object, a total managing object, and three database objects. Roles of these objects are described. The architecture is applied to a practical two mobile robots system performing box pushing in a cooperative way. A single mobile robot is a single functional module and the function of each object of the module in this particular work is explained. Experimental results are shown with discussion.