The present invention has a communication connection means (21) which mutually connects communicatably control units (Ca, Cb) for individually controlling operations of robots (Ra, Rb) to constitute a network, input means (37a, 37b) which are respectively installed in the control units and input operation instructions of the robots, and timing signal generation means (69a, 69b). The control units are selectively set to any one of an independent function execution mode, a master function execution mode, and a slave function execution mode, and among the control units, the control unit (Ca) to perform a master operation is set to the master function execution mode, and the residual control unit (Cb) is set to the slave function execution mode, and by correcting a minimum interruption period (Ts(b)) of the slave side control unit (Cb), a control time (ta11, ta12, ta13) to the master robot (Ra) of the master side control unit (Ca) is delayed by a predetermined time (T) to perform the cooperative operation. By doing this, the control units are always kept in the synchronized state, thus the operations of the robots can be prevented from variations.