Integral value measuring circuit

An integral value measuring circuit comprising:

• an operational amplifier,
• a capacitor connected between an input side and an output side of the operational amplifier,
• wherein an electric potential of an output terminal where a predetermined resistance element is connected to an output side of the operational amplifier is set to zero,
• a positive DC voltage generating circuit and a negative DC voltage generating circuit which comprise a positive power source and a negative power source are provided for the positive power source and the negative power source, respectively, at the output side of the operational amplifier,
• the positive DC voltage generating circuit and the negative DC voltage generating circuit are connected to a positive power terminal and a negative power terminal, respectively, of the operational amplifier through a switch and are connected to the output terminal of the operational amplifier, and
• a connection line between the negative power terminal and the switch of the negative DC voltage generating circuit side being connected to the positive power terminal of the operational amplifier through a cross resistance element having a resistance value negligible compared to a leakage resistance value of the first switch, and
• a connection line between the positive power terminal and the switch of the positive DC voltage generating circuit side being connected to the negative power terminal of the operational amplifier through a cross resistance element having a resistance value negligible compared to a leakage resistance value of each switch.