To obtain a reduction circuit in which the drift of a pressure sensor is corrected at low costs.

An electric charge is generated across a crystal 2 according to a strain clue to an applied voltage. An integrating circuit 3 converts the electric charge generated across the crystal 2 into a voltage. When a reset signal RE is input, a reset circuit 4 resets the integrating circuit 3 so as to cancel a cumulative error. A main cause for a drift is the existence of the leakage current Ia of an FET 23 flowing out from a capacitor 22 and the existence of the leakage current Ib of the capacitor 22 itself. When a diode 5 is added to the input line of a sensor in a reverse bias state, a correction current Ic whose magnitude is identical to that of the leakage current of the sensor and whose flow direction is opposite is supplied from the diode 5.