PURPOSE: To facilitate the maintenance by automatically displaying an associated synchronization executing instruction in the other one of control programs stored in robots if the content of the other one of the control program is required to be known during inspection of one of the programs or the like.

CONSTITUTION: Memory devices 4a, 4B storing therein control programs are provided respectively in robots 10A, 10B. Execution of an instruction to be executed in synchronization with another robot, such as 4A2, is made to stand by until an associated synchronizing operation instruction in another robot, such as 4B2, is executed, and accordingly, the robots are operated being synchronized with each other. In this case, there are provided synchronization initiating instruction pointers 6A, 6B and counters 8A, 8A for counting read-out initiating instructions in order are provided in the respective programs. Further, there are provided counter display programs 9A, 9B for searching the control program in another robot for a group of instructions subsequent to a specified memory position when a specific instruction is designated, and for displaying thereof.