To prevent fabrication and leak of hold data even when a releasing method of a security function is discovered by erasing hold data of a memory means independently of setting of rewriting prohibition information when a read-out prohibition state is released by setting read-out prohibition information.

When releasing a security function (security off) is indicated to a command interface 13, a state machine (erasing means) 14 of a flash memory checks cells 12a to 12c for protection in a protection information/security information storing circuit 12, and judges whether it is in a rewriting prohibition state (protection on) of protection information or not. When it is in a rewriting prohibition state, setting protection information is neglected, hold data of all blocks 11a to 11c in a flash memory main body (memory means) is forcedly erased.