To provide a technique capable of avoiding or reducing the risk of unintended rewriting of a data caused by reading repeatedly the data from a nonvolatile memory.

An access controller part 34 input with an operation switch request signal input from an address comparison part 33 switches an operation from a usual reading access to a normal read access, when a reading address output from a host system 1 in this time is consistent with a reading address output from a host system 1 in the last. That is, the access controller part 34 reading-accesses a memory buffer part 44, without read-access to a memory access array 43. The risk of unintended rewriting is thereby avoided or reduced by reading repeatedly the data stored in the memory access array 43.

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