PURPOSE: To perform a large addressing and a discontinuous addressing, by providing a memory addressing device on the way of an interface line for a data processor and a memory processor and performing a high speed address conversion.

CONSTITUTION: A conversion memory 11 for memory addressing device consists of a prefix and a plurality of address conversion tables. An entry register 14 entries address information transmitted from a data processor, the address information is entried to an entry register 14 with split to upper and lower-order addresses. An entry register 16 stores the upper-order address converted with address conversion tables 1Wn and the lower-order instruction of the address information from the data processor altogether. An entry register 18 stores a converted memory device number with the address conversion table.