PURPOSE: To improve the throughput of a bus without the necessity of excessive time by providing a request transmission means for the transmission-side of transmission-side and reception-side bus controllers and providing a reply response means for the reception-side.

CONSTITUTION: The request transmission means 20 is provided for a transmission-side bus control circuit 10 provided for a transmission-side agent 1 connected to the common bus 100, and the reply response means is provided for the reception-side bus controller 12. The means 20 checks errors for a bus transmission request requested from a high-order unit, gives a bus use right request before the completion of the check of the errors. When the errors are detected, a non-operation code is outputted to a transfer type line 52 on the bus 100. When the non-operation code is received from the line 52 on the bus 100, the means 22 outputs a normal reception code to a response status line 53 on the bus 100. Thus, the throughput of the bus can be improved without the necessity of excessive time.