To enable a microprocessor to surely reload a built-in memory at the time of self-resetting.

According to a prescribed time constant, a terminal voltage Vc is changed by a time constant circuit 3 to be triggered by a self-reset signal outputted by a microprocessor 2, and at this reset timing of the microprocessor 2 reset by feeding back the self-reset signal, the polarity of the terminal voltage Vc is switched. Then, a comparator 12 with hysteresis having a pair of threshold voltages with a hysteresis difference ΔVh discriminates a threshold value with threshold voltages VU and VL corresponding to the change of polarity of the terminal voltage Vc of the time constant circuit 3, and a period sandwiched between a pair of threshold value discrimination outputs preceding and following with respect to time is defined as a reset period.