PURPOSE: To confirm the presence of a device having a simple constitution and the diagnosing result in initialization by using a bus request signal and an initialization signal.

CONSTITUTION: A reset signal output circuit 12 outputs the reset signals (a) to the control parts 21, 31 and 41 of devices 2 - 4 in response to a request of a main control part 11. The parts 21, 31 and 41 output the initialization signals (b) and bus request signals (c) - (e) respectively and then start the diagnoses for initialization. The part 41, for example, detects the abnormality and finishes the diagnosis. Thus the part 41 stops the output of the signal (b) while outputting the signal (e). Then an initialization signal monitor circuit 13 detects the stop of the signal (b) and gives the report to the part 11. The part 11 stops a priority deciding circuit 14 from monitoring the signal (e) and inhibits the use of a bus to the part 41. Thus it is possible to confirm a specific control part that finishes normally or abnormally the diagnosis.