PURPOSE: To rationalize the processing of data exchange or the like by providing an access means to a shared memory suitable in the case of being provided with at least three systems of microprocessors.

CONSTITUTION: This device is provided with the microprocessors 3A, 3B and 3C, local memories 4A, 4B and 4C used independently by the respective microprocessors 3A, 3B and 3C, the shared memory 6 shared and used by the respective microprocessors 3A, 3B and 3C, a selector part 5 for selectively connecting the buses 12A, 12B and 12C of the shared memory 6 and the respective microprocessors 3A, 3B and 3C and a mediation circuit 7 for generating control signals for connecting the buses 12A, 12B and 12C of the shared memory 6 and the respective microprocessors 3A, 3B and 3C to the selector part 5. The respective microprocessors 3A, 3B and 3C are provided with a means for issuing an access request to the shared memory 6 to the mediation circuit 7 and the mediation circuit 7 is provided with the means for monitoring the access request and mediating the enable/disable of access.