PURPOSE: To obtain easily square waves having the frequency corresponding to twice or more the frequency of an input signal source by taking out prescribed- shaped outputs from an output terminal constituted so that the output is taken out by turning on/off a switching transistor (TR) by a rectified and composed output.

CONSTITUTION: Diodes D1, D2, D3, D4 rectify outputs generated from both ends of the secondary winding of a transformer T1 and the output terminal of a phase turning circuit and diodes D5, D6 rectify the full wave of the voltage between both ends of the secondary winding of the transformer T1. Respective voltage waveforms V1, V2, V3, V4 are rectified at their half-waves by the diodes D1, D2, D3, D4 and composed with each other at their output terminals. The voltage waveforms V5, V6 are impressed to switching TRs Q1, Q2 respectively. Therefore, the TRs Q1, Q2 are controlled on/off by the composed voltages V1, V6 respectively, and only when both TRs Q1, Q2 are turned on simultaneously, the potential V7 of a connection point between a resistor R5 and a diode D7 is turned to the low level. Consequently, a square wave with the frequency corresponding to twice the frequency of the input signal source E1 is obtained.