1. An instruction fusion calculation device comprising: an instruction fusion detection circuit to determine 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 to fuse 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; a calculator to execute 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; and an instruction passing circuit for changing an order of execution of instructions so that when another instruction exists between the preceding instruction and the subsequent instruction to which it is determined that the instructions can be fused in an instruction sequence, the subsequent instruction is executed before executing the another instruction.