PURPOSE: To make the value of an equivalent inductance accurate by using two sets of switched capacitors so as not to connect both the capacitors to the same terminal by means of the switch control at the same time.

CONSTITUTION: Two switched capacitors comprising switches S3, S3', a capacitor 3 and switches S4, S4' and a capacitor 4 are provided. The switches S3, S3' and S4, S4' are controlled to connect one of the capacitors 3, 4 to input terminals 1, 2, while buffers 5, 6 are connected to respective output terminals 10, 11, the capacitors 3, 4 are not connected to the same terminal. Thus, an electric charge flows between signal terminals over the entire period of the sampling period and an error due to the interruption of the flow of electric charge is generated and the equivalent inductor of the non-grounded switched capacitor is made accurate.