In a cache memory simultaneously conducting updating for a miss and a decision on a miss for the subsequent address, a write flag generated by a control unit is written in a valid flag field. Based on this operation, during an access to an external memory at an occurrence of a miss, a tag field and the valid flag field are simultaneously updated. When updating a data field, a read operation is achieved on the tag and valid flag fields to decide occurrence of miss. Thus, an external memory access for a miss at a next address can be executed at an earlier point of time. Moreover, by the provision of a data latch disposed for an output from the data field, and by reading data at a next address and keeping it in the data latch during a memory read cycle, succeeding hit data can be outputted immediately after a miss processing is completed. Furthermore, also in a cache memory having a plurality of tag fields and a plurality of valid flag fields, the updating for a miss and the decision on a miss for a next address can be attained at the same time.