PURPOSE: To speed up address conversion by converting a virtual address into a physical address, holding it and starting the conversion of virtual address which is inputted later while the physical address is outputted.

CONSTITUTION: An address conversion means 11 sequentially converts a virtual address A which is time-sequentially inputted into a physical address B. A physical address holding means 12 holds the physical address B and outputs the held physical address to a memory device as a physical address C. A physical address update means 13 updates the content of the holding means 12. An address conversion start means 14 starts the address conversion of the virtual address A which is inputted later than the virtual address corresponding to the physical address C. Namely, the conversion of a virtual address A2 is started while a physical address C1 corresponding to the virtual address A1 is outputted, and a physical address B2 is obtained.