To reduce the circuit-technical cost at the time of arithmetic coupling of an analog signal and a digital signal by providing a controllable polarity switching element which allows the analog signal to pass with the changed or unchanged polarity in accordance with control of a sigma-delta modulator.

Offset-compensated voltage signals are supplied to controllable polarity switching elements 6 respectively. They can connect or transmit signals with changed polarities or unchanged polarities, namely, switched polarities. The control of the switch 6, namely, the control to change or not change the polarity is performed by using a digitally controlled sigma-delta modulator 8. For example, the analog signal applied to the switch doesn't have the polarity changed when signal +1 is applied to the control input side of the switch 6, and it has the polarity changed when signal -1 is applied there; and thus, multiplication between the analog signal and the signal existing in a digital form is possible in average.