A microcomputer includes reloadable registers for prestoring count values corresponding to an ineffective interval and an effective interval which are set in accordance with the timing of a first edge and a second edge of a head pulse signal, and for setting these count values sequentially into a counter. Only when the first edge and second edge are input at predetermined timing through an event input terminal, that is, only when the head pulse signal is input, the interrupt signal is generated for changing the operation mode from a low current consumption mode to a normal operation mode. This makes it possible to prevent a mode transition due to noise, and reduce the power consumption of the microcomputer by making more effective use of the low current consumption mode by improving a mode transition identification rate.