PURPOSE: To save the memory for an address table for storing the start address of a program.

CONSTITUTION: The start address of the program which is represented with three bytes is shifted by one bit to the right and its low-order two bytes are stored in the address table. When the program is executed, the necessary start address is selected in the address table according to the execution conditions, the value is shifted by one bit to the left to obtain a two-byte offset value, and a base address α$000000' or '$010000' which is previously set is combined to depress the original start address, so that the program is executed with this start address. The address table is reduced to 2/3 times as large as before and the memory can be saved. In this case, even if the number of bytes slightly increases as a result of the depressing process, that is very small as compared with the compression effect of the address table and there is no problem.