By connecting, to a bus bridge according to a configuration of a bus system, a monitor circuit including an activation control circuit generating a counter activation signal from an input monitor activation signal, a counter circuit, activated by the counter activation signal, counting the transfer number using a signal of bridge transfer completion indicating an issuance of one transfer from a bus bridge, and outputting a count completion signal when the transfers of the same number as that stuck in the bus bridge indicated by the signal of the transfer number stuck in the bridge is issued when being activated, and a completion control circuit outputting a monitor completion signal upon receiving the count completion signal from the counter circuit, consistency of data may be guaranteed in any bus system without changing the configuration of the bus bridge based on the number of masters accessing the bus bridge.