PURPOSE: To realize an ultra-miniature size for the relay by leading each AC input smoothed through the rectifier circuit to the adder input terminal of the adder integrating circuit via the operational amplifier.

CONSTITUTION: Absolute value comparator circuit 8 of the static relay gives the arithmetic amplification to output e1 and e2 of full wave amplifier circuit 1 and 2 via adder-type integrating circuit 10 composed of arithmetic amplifier 9 and supplies output e0 to voltage level detector 7. Resistance 11 (resistance value Rf) and capacitor 12 (capacity Cf) are connected in parallel to amplifier 9, and output e1 and e2 are supplied to operator 9 with the reverse polarity and via resistance 13 and 14 (resistance value R1, R2) to obtain the output shown in Eq. [I]. In other words, circuit 10 delivers the smoothed wave (degree of smoothness decided by CfRf) which is shown in the member of CfRf(de0/dt) of Eq. [I]. Rf can be set sufficiently high in the range where the ratio between R1 and R2 becomes more than a fixed level, so Cf can be set low enough. Also, the input-output ratio can be set freely for circuit 10 according to Eq. [I], it is clear that the amplifier is not required even in case AC input E1 and E2 are minute. Thus, the size of the relay can be minimized.