A duplex memory control apparatus having a first control unit containing a first memory and a second control unit containing second memory, a first control unit and a second control unit connected to each other through a bus. The first control unit having a central processing unit writing write data in the first memory; a transmitter obtaining the write data to be written in the first memory by the central processing unit, a transmitter, when a write data can be specified based on another write data previously obtained, transmitting specific data smaller than a write data to the second control unit instead of the write data; a first bus mutually connecting the central processing unit, the first memory an the transmitter; a first direct memory access unit reading the write data held int eh first memory through the first but; a second bus connected with a first direct memory access unit; and an access limiter connected to the first bus and the second bus and limiting to use the first bus by the first direct memory access unit when the central processing unit uses the first bus. The second control unit having a data producing section receiving the specific data from the transmitter and producing an original write data based on the specific data; and a second direct memory access unit writing the original write data produced by the data producing section into the second memory.