PURPOSE: To simplify a circuit by giving a threshold characteristic to a circuit (point) to be controlled and selectively driving the circuit to be controlled with the aid of a drive signal having an asymmetrical waveform.

CONSTITUTION: The one s1 out of the secondary terminals of a transformer T is connected to the one OP1 out of drive output terminals on a positive side and the one ON1out of drive output terminals on a negative side. The other s2 out of the secondary terminals is connected to the other OP2, out of the drive output terminals on the positive side and the other ON2 of the drive output terminals on the negative side. A 1st device to be controlled LDP responding when the potential of the terminal OP1 corresponding to the terminal OP2 exceeds a positive fixed value (threshold VTP) is connected to the drive output terminals OP1 and OP2 on the positive side, while a 2nd device to be controlled LDn responding when the potential of the terminal ON1 corresponding to the terminal ON2 exceeds a negative fixed value(threshold VTN) is connected to the drive output terminals ON1 and ON2 on the negative side. When AC signals are impressed on control input terminals I1 and I2, the secondary sides s1 and s2 of the transformer T generate signals in response to that impression.