PURPOSE: To improve the resolution of an output signal by sending out an up signal in each case wherein the level states of two pulse signals inputted in out-of-phase relation change cyclically among the 1st∼the 4th modes and sending out a down signal in each case wherein they change cyclically in the opposite direction from said direction.

CONSTITUTION: Signals which vary in a positive or negative direction according to the clockwise or counterclockwise rotation of a rotary encoder (not shown in figure) are inputted to input terminals 9a and 9b of a decoder 9, which outputs a level '1' from one of output terminals Q0∼Q3 according to the level states of the input signals. For example, when the output Q0 of the decoder 9 is 'l', a flip-flop circuit(F.F) 11 is set and an F.F 12 is in a set signal waiting state. The output of an OR gate 13 is held at '1' and the output of an OR gate 14 is held '0' through AND gates 10a∼10h and delay circuits 15a∼15d. Even when the encoder rotates counterclockwise, similar results are obtained. Consequently, four up or down signals are obtained in every period of the input signals.