A data coincidence detecting circuit including a register for receiving n-bit data, a counter for counting up until 2.sup.n to compare the n-bit data with it, a comparator for comparing the outputs of the register and the outputs of the counter, respectively to generate a coincidence detecting signal, a mask portion connected to the output of the comparator for masking the period from a time point when the n-bit data is input to a time point when the input of data ends, and a logic circuit for logically adding the output of the mask portion and the output of the comparator to output the result.