A voltage detecting circuit comprises: an operational amplifier whose one input terminal is applied with a first reference voltage; a first capacitor whose one end is connected to the other input terminal of the operational amplifier; a second capacitor whose one end is connected to an output terminal of the operational amplifier, and whose other end is connected to the other input terminal of the operational amplifier; a switch circuit for applying a first voltage and a second voltage sequentially to the other end of the first capacitor; and a discharging circuit for discharging the second capacitor before the second voltage is applied to the other end of the first capacitor, a difference between the first voltage and the second voltage being detected based on a voltage at the output terminal of the operational amplifier after the second voltage is applied to the other end of the first capacitor.