1. An instruction code conversion apparatus converting a first code to a second code longer in bit length than said first code to create an instruction code including said second code, comprising: a storage unit storing therein information provided for converting said first code to said second code; and a conversion unit connected to said storage unit, receiving said first code and a third code, converting said first code to said second code based on said first code and said stored information, determining a fourth code from said second code and said received third code, and creating an instruction code including said second and fourth codes.