Reference logical data is spatially divided by a data dividing circuit for each time slot, and the divided data are converted into data, each having a continuous effective period. The divided and converted reference data and input logical data are compared by comparators to detect whether or not they are coincident with each other. A clock signal for determining the timing of comparison is also divided by a clock signal dividing circuit into n clock signals which are displaced one time slot apart in phase and occurring with a period of n time slots. By these divided clock signals those of the outputs from the comparators corresponding thereto are taken out from a comparison output circuit.
