A program stored in a memory is read, and in a path representing the order of processing instruction sequences forming the program, a subgraph including a sequence of instructions that includes only one instruction at the entry and only one instruction at the exit is identified. At least a part of a source instruction sequence included in the subgraph is extracted as a new program block and stored in a memory. An instruction for calling the instruction sequence in the new program block is inserted in a program block including the source instruction sequence. The program block including the source instruction sequence is then stored in the memory.