In order to increase the operation efficiency of the operation register for holding store data when executing store instruction to store data in a predetermined store area on the main memory or the cache memory, in the present invention, an instruction processing section is adapted so as, when an operation register holding the operation result is determined, causes the operation result to be issued from the operation register to store buffers as store data; when the store data are held by the store buffers before the store instruction is held by store ports, a restraint section restrains a reset section from setting a store data hold flag to OFF at a point of time when the store instruction is held by the store ports to maintain the store data hold flag to ON.