To execute processing by a processor during data input/output.

A processor 111 fetches the data from an input buffer memory 112, performs an arithmetic processing by a specified program and outputs the resultant data to an output buffer memory 113. Both of the input buffer memory 112 and the output buffer memory 113 have a double-buffer structure, each of them has areas A, B and holds input/output data for the processor 111. Reading, writing of the input buffer memory 112 and output buffer memory 113 are controlled by a DMA 114 according to the processing state of the processor 111 and the data input/output is performed even during the arithmetic processing of the processor 111.