PURPOSE: To minimize disconnection of an execution program when trouble occurs in a standby system memory by setting the interruption source when a standby memory trouble counter overflows and making interruption processing.

CONSTITUTION: When an access signal is generated in the access line 101 of a processor 10, a memory controlling circuit 301 is started through the 104 in an act system memory 10 and by the 106 in a standby system memory 30, and makes memory access to a memory module 300. When trouble is generated by this access, a trouble detecting circuit 302 is started. The output starts a trouble counter and overflow circuit 102 of the processor 10 by a controlling line 103. The trouble counter and overflow circuit 102 are started if trouble occurs at each memory access. When the condition of overflow of the trouble counter is brought about, an interruption source circuit 100 is started.