INFORMATION PROCESSOR

PURPOSE:To increase the efficiency of instruction processing, by making an instruction buffer ineffective only when the changed content is executed as the instruction, when the content fetched to the instruction buffer is changed in a memory. CONSTITUTION:An instruction readout (IF) control of an instruction control unit IU1 is started from an operation unit EU2, an IF request 7 and an IF address 8 are given from the IU1 to a storage control unit SCU3, the control of the SCU3 and a main storage device MS4 is started, an instruction data 9 is read out from the MS4 and fetched to the instruction buffer of the IU1. When the content advance-fetched in the instruction buffer is changed on the MS4, the change in the instruction is detected based on a readout address to the instruction buffer, an execution instruction address, byte location information of the executed instruction, a stored address by the storage instruction, and byte location information changed by the storage, and when the changed instruction is executed, the instruction buffer is made ineffective, allowing to reduce unnecessary readout from the memory.