In this paper, a power reduction technique which merges frequently executed sequences of object codes into a set of single instructions is proposed. An instruction decompressor restores the merged sequence of object codes before decoding the object codes. A ROM implements the decompressor. In many programs, only a few sequences of object codes are frequently executed. Therefore, merging these frequently executed sequences into a single instructions leads to a significant energy reduction. Our experiments with actual read only memory (ROM) modules and some benchmark program demonstrate significant energy reductions up to more than 65% at best case over a instruction memory without the object code merging.