PURPOSE: To realize a flip-flop circuit which has a function of an inverter in addition to its normal working, by using a control circuit which always sets a circuit of one side under an open state regardless of an input signal.

CONSTITUTION: NAND circuits N1 and N2 which function as the 1st circuit containing the input and output connected in a crossed state to each other have an R-S type flip-flop (FF). NAND circuits N3 and N4 are added to the input of the 1st circuit to form a J-K type FF1. Then the output of a gate circuit G1 is connected to the input of the circuit N2 to form a control circuit 2 which sets the circuit N2 under an open state regardless of the input signal. Thus an overall FF circuit is obtained. This FF circuit functions as a normal J-K type FF when the control signal is 0 and then as a mere inverter when the control signal is 1 respectively. Such FF circuits are combined to easily form a variable frequency dividing circuit.