In adjustment processing executed at the same period as waveform analysis processing, a CPU of a microcomputer permits an execution of the waveform analysis processing on condition that the waveform analysis processing has been completed. Thus a period of non-execution of the waveform analysis processing is ensured between a completion of preceding waveform analysis processing to an execution of next waveform analysis processing. Since low priority processing, which has been disabled to be executed, is enabled to be executed, it is possible to stop continuation of disablement of execution of the low priority processing.