Four semiconductor strain gauges constitute a bridge circuit. This bridge circuit and a sensitivity temperature compensation circuit are connected in series, and a constant voltage is applied to the series circuit. The sensitivity temperature compensation circuit varies a voltage across the bridge circuit, depending upon temperatures. The constant voltage is divided to produce a predetermined voltage. The predetermined voltage is selected to be equal to the voltage of one output side node of the bridge circuit at the time when the semiconductor strain gauges are unstrained and at a predetermined temperature. The point of this voltage and the output side node are connected through a resistor so as to perform zero-point temperature compensation.