1. A cache system comprising: a cache data memory for storing a part of data stored in a main memory; a cache tag memory for storing information indicating a position of the data stored in the cache data memory, in the main memory; a cache tag buffer for storing a part of information of the cache tag memory and cache control means that controls an access to the cache data memory; wherein said cache control means retrieves both of the cache tag memory and the cache tag buffer when cache control receives a memory access request and uses the information of the cache tag buffer to control an access to the cache data memory when a target cache block of the memory access request is stored in the cache tag buffer.