PURPOSE: To arbitrarily enable a set address to be changed by storing the set address written in an input/output port by a master device in a latch, and com paring it with an address on a system bus.

CONSTITUTION: When the master device 10 writes the set address on the input/ output port 2 provided in each of slave devices 11W14 as a data, the set address is stored in the latch 3, and by comparing the address on the system bus 1 outputted from the master device 1 afterwards, with the set address stored in the latch 3, an address coincidence signal is generated. Also, by rewriting the set address by the master device 10, a new address coincidence signal for a new address coinciding with a rewritten set address is generated. In this way, it is possible to change the set address arbitrarily.