PURPOSE: To maintain a good proportional relation between the output voltage of a strain gage bridge and an aplied source voltage over a wide range by compensating the characteristics of the change in the output voltage of said bridge by said source voltage.

CONSTITUTION: When a source voltage Vcc rises, the temp. elevation of strain gages SG1, SG3 disposed in the central part of a silicon diaphragm is higher than the temp. elevation of the strain gages SG2, SG4 disposed in the peripheral part. Thus the output voltage of a strain gage full bridge FB supplied to the +input terminal of an operational amplifier OP1 deviates to a -side and the output voltage of the bridge FB supplied to the +input terminal of an operational amplifier OP2 to a +side respectively. The point of connection between resistors R6 and R7 is supplied to the +input terminal of an operational amplifier OP3 via a resistor R8, so that a deviation is generated in the direction decreasing from the proportional relation with the voltage Vcc. Thus the output voltage converted to pressure proportional to the source voltage is obtained stably.