PURPOSE: To set the protection of a memory and to check the protection with a simple constitution, regardless of the mixed presence of ROMs and RAMs, by providing a protection set means corresponding to each of memories.

CONSTITUTION: A memory chip selection circuit 1 introduces a specified selection signal to a output terminal corresponding to the number of memory chips and a protection set circuit 2 has a protection set means corresponding to each of a plurality of memories and transmits a specified protection signal. The selection and protection signals are applied to a matrix circuit 3, and if a selection signal of the memory chip not protected is applied to the circuit 3, the signal is outputted via a memory chip connection circuit 4. Further, when the selection signal of the memory chip to be protected is applied, a protection error signal PE is given from a protection control circuit 5 consisting of electronic switches and the selection signal is not transmitted from the circuit 4.