PURPOSE: To prevent surely the free-funning oscillation by applying in advance a DC offset so that 2-signal of a master flip-flop and a slave flip-flop is inputted when the hold side of a differential switch of each flip-flop is in a no-singal input state.

CONSTITUTION: A DC offset V0' is provided to base potentials of transistors(TRs) Q21, Q22, that is, potentials P2', P1' corresponding to emitter followers E1, E2. Thus, the TR Q2 is turned on and the TR Q1 is turned off in a 1st differential switch circuit S1 in the no-signal input state, the TR Q9 is turned on and the TR Q10 is turned off in the 4th differential switch circuit S4. Thus, the free-running oscillation is prevented for both the master flip-flop A1 and the slave flip-flop A2.