1. An instruction fusion calculation device comprising: an instruction fusion detection circuit for determining whether or not fusion of a preceding instruction and a subsequent instruction located after the preceding instruction that have a flow dependence relationship can be made; an instruction fusion circuit for fusing the preceding instruction and the subsequent instruction to which it is determined by said instruction fusion detection circuit that the instructions can be fused into one instruction; and a calculator for executing the one instruction into which the instructions are fused by the instruction fusion circuit to output the calculation result and outputting at least one of the calculation results obtained by executing the preceding instruction and the subsequent instruction as an intermediate result.