INSTRUCTION FETCHING DEVICE

PURPOSE:To precisely detect an error by simple constitution at the time of fetching an instruction. CONSTITUTION:A microprogram is stored in a storage part 22 and check data having plural instructions and the same values as addresses are integrated in the microprogram as data. At the time of reading out the data from the storage part 22 as reading data, an instruction executing part 23 judges whether read data are an instruction or not. When the data are not an instruction, an address data comparing part 24 compares the read data with the value of an address corresponding to the reading data and generate a compared result. An abnormality judging part 25 judges whether abnormality exists in the reading data or not based upon the compared result, and when abnormality is included, sends an error signal.