PURPOSE: To shorten an access time by making a read-out method of a serial memory of RAM constitution a pipeline system.

CONSTITUTION: A serial memory having RAM constitution is a FIFO buffer memory, has plural memory cell arrays 4, 6 having plural cells, and data elements are read out in the same order as the order with which it is written in a memory. A memory cell is selected by a read-out array selector 20 and a read-out cell selector 22 to read out data elements in each readout cycle. At the time, a data element read out from a memory cell is not a element to be outputted with the present read-out cycle, but is a element to be read out at the next cycle. By using the pipeline system, time delay for detecting and selecting a memory cell is prevented, and an access time is shortened.