A storage holds instructions including a branch instruction and a corresponding branch destination instruction. The instructions are sequentially fetched from the storage to a decoder. The decoder sequentially decodes the fetched instructions and derives commands from the respective instructions. The commands are sequentially transferred from the decoder to an execution unit. The execution unit sequentially executes the transferred commands. The decoder serves to detect the branch instruction. When the branch instruction is detected, a normal instruction fetching process is interrupted and the branch destination instruction is promptly fetched to the decoder. The decoder prevents a command of the branch instruction from being transferred to the execution unit.