PURPOSE: To prevent a control circuit from being complicated even when the number of words is increased and to easily change the number of words by executing a first-in first-out function by providing a data holding means and an address control circuit corresponding to the number of words.

CONSTITUTION: At the time of writing data on a memory 20, '1' (or '0') is written on the data holding means (22-0W22-n) simultaneously, and '0'(or '1') is written simultaneously at the time of reading out the data. And the contents of the data holding means (22-0W22-n) are read by the address control circuits (23-0W23-n), and the first-in first-out function is executed by controlling the write address of input data and the readout address of output data. Since the numbers of the data holding means 22 and the address control circuit 23 corresponding to that of the of words are provided, the change of the number of words can be performed by changing those numbers. In such a way, it is possible to prevent the control circuit 23 from being complicated, and to change the number of words easily without changing the constitution of the circuit remarkably.