An integral value measuring circuit includes an operational amplifier and a capacitor connected between input and output sides thereof, an electric potential of an output terminal where a predetermined resistance element connected to an output side of the operational amplifier is being zero, positive and negative DC voltage generating circuits which comprise positive and negative power sources, respectively, at the output side of the operational amplifier, the positive and negative DC voltage generating circuits and being connected to positive and negative power terminals, respectively, of the operational amplifier through switches, and a connection line between the negative power terminal and one switch and a connection line between the positive power terminal and another switch being connected to the positive and negative power terminals, respectively, of the operational amplifier through cross resistance elements having resistance values negligible compared to a leakage resistance value of the switches.