PURPOSE: To prevent the oscillation of a flip-flop circuit due to a parasitic PNP transistor (TR) by detecting the power supply voltage drop so as to cut off a current to a TR constituting the flip-flop circuit.

CONSTITUTION: When a +VCC power supply is lowered, a control signal SC is obtained from a voltage level detecting circuit 14 and a TRQ31 is switched to the ON-state. Thus, a current flows from the +VCC power supply via a resistor R25 and the TRQ31. Further, a TRQ23 is turned off, the positive feedback operation of the flip-flop circuit 12 is stopped forcibly and the oscillation is prevented. Even if the power voltage is decreased to a value being a prescribed voltage or below in this way, the generation of oscillation is prevented in advance, then a TR circuit capable of driving a radio cassette and a tape recorder or the like at a low voltage power supply is obtained.