PURPOSE: To prevent malfunctions, by inverting an operating FF at the time when another counting circuit reaches a prescribed count value from the inversion time in case that an FF which outputs a countenable-signal is inverted.

CONSTITUTION: If a D type FF F1 is inverted through an inverter 12 and an AND gate 13 at the time when 4-bit binary counters 2∼4 count, for example, 2048 clock pulses CLK, a binary counter 11 is substituted for counters 2∼4 to count pulses CLK after the FF1 is inverted. Thus, if a D type FF6 is inverted when the counter 11 counts 8 pulses CLK, the FF6 is inverted when a desired number of pulses CLK is counted.