A microcomputer includes a main oscillator for generating and outputting a main clock signal, a sub oscillator for generating and outputting a sub clock signal, a central processing unit that operates based on the main clock signal, a signal output circuit that operates based on the sub clock signal and outputs a timing signal at a predetermined interval, and a voltage monitoring circuit that operates based on the sub clock signal and intermittently performs a voltage monitoring function in response to the timing signal. The sub oscillator operates independently of the main oscillator.