To make judgeable the moving direction of an object optically in a noncontact method even if the inspection object has no geometric structure.

The moving object is irradiated with laser light, and scattered light is split in two, and each beam is received through a space filter having a phase difference of about 90 degrees, to thereby acquire two signals A, B. After removing low frequency components therefrom by high-pass filters 22a, 22b, the signals are binarized by comparators 23a, 23b, and then the time average is determined relative to an output pulse of a phase direction discrimination circuit 24 comprising two D-flip-flops 24a, 24b for discriminating advance or delay of the phase of binary signals Da, Db from the comparators 23a, 23b, and generating the pulse. The moving direction is judged from the value.