In network communication system, a master unit's controller transmits a command signal to a CXPI bus. The controller specifies values of turning-on intervals of loads as delay time lengths in a delay area of the command signal, and specifies ports of slave units in an output port specification area in a specified order corresponding to turning-on order of the loads. The microcomputer of each slave unit receives the command signal from the CXPI bus. The microcomputer acquires a specified number of a port of the own slave unit specified as an instruction target in the output port specification area, integrates specified values in the delay area, and outputs the operation signal to the specified port at a timing delayed from the reception of the command signal by the time length calculated by the integration. The number of specified values is a number obtained by subtracting 1 from the specified number.