Disclosed is a compiler apparatus for generating an instruction code composed of instruction sets each including an instruction that designates an m-bit immediate value indicating a location of a data item in a memory area. The compiler apparatus sequentially selects, based on one data attribute, a data item from a group X composed of a plurality of data items; and judges, each time a data item is selected, whether the selected data item is allocatable to an n-byte memory area (n.ltoreq.2.sup.m). When the judgment is negative, the compiler apparatus specifies, based on a different data attribute, a data item out of all the selected data items and excludes the specified data item from the group X, and repeats the selection until all the data items remaining in the group X after excluding specified data items are judged to be allocatable to the memory area.