A frequency converting unit 101 includes a connection circuit for connecting a plurality of inverting circuits through which a delay time between an input signal and an output signal is changed according to a magnitude of the signal output by the image pickup unit, and one or a plurality of switch elements which are connected between an output terminal of the inverting circuit and an input terminal of another inverting circuit not adjacent to the inverting circuit, and generates a clock signal having a frequency according to the connection circuit. The control unit 20 controls the switch elements included in the frequency converting unit 101 to open and close. The count unit 103 counts the clock signal generated by the frequency converting unit.