A memory managing unit manages a memory where a code is stored and makes valid the memory where the code to be executed is stored so as to instruct a processor to execute the code. The memory managing unit stores verifying key used for verifying the code in a verifying key holding unit. When the code is stored in the memory and becomes executable by the processor, the memory managing unit verifies the code using the verifying key held in the verifying key holding unit and verification information attached to the code. If the code is verified, the memory managing unit makes the memory valid; if not, if performs control so as not to make the memory valid.