A bias potential generating circuit includes a clock supply circuit that generates a clock signal having a predetermined frequency; a rising sine wave generating circuit that generates a rising wave form signal having a wave form of a rising portion of a sine wave; a ΔΣ conversion circuit that generates a pulse width modulation signal by pulse width modulating the rising wave form signal; a first resistor, one end connected to a reference potential input terminal of an operational amplifier; a second resistor, one end connected to the first resistor and to the reference potential input terminal of the operational amplifier, and the other end being grounded; and a switch connected to a power supply and to the other end of the first resistor, the switch being turned ON and OFF by the pulse width modulation signal.