PURPOSE: To attain regular transition of a state by synthesizing the decoding signals sent from plural decoders into a single signal by an OR circuit and then controlling a Johnson counter.

CONSTITUTION: An OR circuit 8 synthesizes the decoding signals 3a-3d sent from the decodes 2a-2d, and a synthetic signal 8a sent from the circuit 8 is applied to the AND circuits 4a-4d provided on the precedent stages 6a and 6b of the JK flip-flops 6a and 6b. Thus a Johnson counter is controlled when the signals 3a-3d are synthesized into a single signal 8a by the circuit 8 and the signal 8a is applied to the circuits 4a-4d respectively. The Johnson counter is also controlled when the signal sent from a 1-shot pulse generating circuit is applied to the circuits 4a-4d respectively.