PURPOSE: To input the action signal of a 2n bit to a loop counter 20, to lengthen the time extension and to improve the action detecting accuracy even when the action signal of an (n) bit is inputted.
CONSTITUTION: The action signal of a 2n bit is converted to a maximum value circuit 18 from a maximum value circuit 12 and converted to a 2n bit. The action signal of the 2n bit from the maximum value circuit 18 is attenuated to the prescribed value by a loop counter 20 of a feedback loop 19 and fed back to the maximum value circut 18 in the 2n bit condition. Two action signals are compared by the maximum value circuit 18 and the higher order (n) bit of the larger action signal is inputted to a maximum value circuit 28. They are compared with the action signal from an input terminal 14, and the larger signal is outputted as the time extending action signal.