and all of each of the a phase and b phase signals 1a and 2a in the foregoing the explanation of operation in the case where the rotatory body rotates in the reverse direction has been mainly made by use of fig7 and 8 though the explanation of operation in the case of the rotation in the reverse direction has been partially made next the explanation of operation in the case where the rotatory body rotates in the reverse direction will be further made by virtue of waveforms shown in fig9 the operation in the case of the reverse rotation is the same as that in the case of the forward rotation but in a region x 2 where the a phase signal 1a is in the level of 34 0 34 and the b phase signal 2a is in the level of 34 1 34 since all the q 1a q 2a q 3a and q 4a outputs 3b 3c 3d and 3e of the shift register 3 are 34 0 34 all the outputs 8a 12a 13a and 10a are also 34 0 34 this is better illustrated in fig9 various outputs 7b 8b 12b and 13b shown in the logic circuit diagram of fig7 are as shown in fig9 therefore the direction signal 5c the direction discrimination signal 12b and the count pulse 13b assume waveforms as shown in fig9 thus since the rotation direction is discriminated by.