PURPOSE: To enable the offsetting of an amplifier voltage and the compensating of temperature changes by switching the first and second signals supplied from a sensor between the first and second amplifying means.

CONSTITUTION: A pressure sensor 10 is provided with inputs 1 and 3 and differential outputs 2 and 4, and the outputs 2 and 4 are connected to two switches 21 and 22. The switch 21 is connected to one input 31 of an operational amplifier 30, and the switch 22 is connected to one input 41 of an operational amplifier 40. These amplifiers 30 and 40 are connected to the input channels 51 and 52 of a microcomputer unit(MCU) 50 respectively, and the control output 53 of the MCU 50 controls the switches 21 and 22 via control inputs 20 and 29. Then the MCU 50 reverses these inputs by switching between the switches 21 and 22, the output 2 is connected to the amplifier 40 via the switch 22, and on the other hand the output 4 is connected to the amplifier 30 via the switch 21. The output voltage V1C of the amplifier 30 is accumulated in digital form in a register R1C in the MCU 50, and the V2C of the amplifier 40 is in a register R2C.