PURPOSE: To reduce a pipeline in size by forming a register group for storing only data for partial writing independently of the pipeline.

CONSTITUTION: Since respective registers in the pipeline 20 have no function for storing partial writing data for a partial writing access request and control information such as an intra-word position or the like of the data, each register is constituted by the number of bits reduced from the ordinary one by the number of bits corresponding to the function. Out of an access request information selected by a priority selecting circuit 10, a storage address and writing data for an allword writing request are set up in an address register 11 and an error correction code circuit 12 respectively. When the kind of the request access is partial writing access, the partial writing data are set up in an input register 21 without being inputted to the pipeline 20.