PURPOSE: To output a rectangular wave even to a capacitive load by connecting the collectors of the 1st and the 2nd transistors (TR) to the bases of the opposite TRs through capacitors respectively, and also connecting the collector of the 3rd TR to the base through a resistance.

CONSTITUTION: The bases and collectors of NPN TRs 1 and 2 are connected to one terminal of a DC power source 12 through base resistances 4 and 5 and collector resistances 7 and 8 respectively, and the collectors are connected to the bases of the opposite TRs 2 and 1 through the capacitors 10 and 11. Further, PNRTR3 is provided; the emitter is connected to the plus terminal of the power source 12, the collector is connected to the collector of the TR1, and the base is connected to the collector of the TR2 through the parallel circuit of a base resistance 6 and a speed-up capacitor 9. Then, an output signal is obtained from the collector of the TR1. Consequently, a voltage close to an ideal rectangular wave is outputted even when the capacitive load is connected.