A starter circuit includes a start detection circuit for detecting a change of an input signal and outputting a start digital signal, a digital OR circuit for outputting a determination digital signal based on the start digital signal, a power supply circuit being activated based on the determination digital signal, and a digital control circuit being operated based on a power from the power supply circuit. The digital control circuit inputs a retention signal to the digital OR circuit for maintaining an operation of the power supply circuit and a reset signal to the start detection circuit for resetting the start detection circuit.