PURPOSE: To effectively process the memory starting actions to each memory area by providing a holding circuit which holds the data received from a control part as the memory start information.

CONSTITUTION: When the start information on the reading actions to the same memory area as all writing actions are held by a holding circuit 8 of a start information holding circuit group 1, a priority order deciding circuit 2 selects all writing actions and sends the address data to a buffer memory part 6 to write it there. The data stored in the part 6 are sent to the circuit 8 via a buffer control part 7 in the written order and held as the write data. The write data serving as the start information is selected by the circuit 2 based on a command of the part 7 or a prescribed rule and written into the corresponding memory area. When a reading action is carried out to the same memory area as a writing action before the writing action is not finished yet via the circuit 8, the contents of the part 6 are read out and outputted.