The data processor enhances the bus throughput or data throughput of an external memory, when there are frequent continuous reads with a smaller data size than the data bus width of the external memory. The data processor includes a memory control unit being capable of controlling in response to a clock an external memory having plural banks that are individually independently controllable, plural buses connected to the memory control unit, and circuit modules capable of commanding memory accesses, which are provided in correspondence with each of the buses. The memory control unit contains bank caches each corresponding to the banks of the external memory. Thereby, the data processor enhances the bus throughput or data throughput of the external memory, since the data processor stores the data read out from the external memory temporarily in the bank caches and to use the stored data without invalidating them, when performing a continuous data read with a smaller data size than the data bus width of the external memory.