1. An instruction generation apparatus which generates an output process instruction group including a plurality of instructions to be executed by a computer, said apparatus comprising: a memory; a branch-instruction generating unit configured to generate, as a part of the output process instruction group, a branch instruction which causes a processing route to branch to a first process instruction so that the computer executes the first process instruction, the first process instruction causing the computer to assign data to an assign-target variable; and a dependent-process-instruction generating unit configured to generate, as a part of the output process instruction group, a dependent process instruction dependent on the data assigned to the assign-target variable, the dependent process instruction causing the computer to execute a predetermined process in the output process instruction group onward when the data indicates predetermined contents, and the data assigned to the assign-target variable indicating a result of the first process instruction executed by the computer according to the branch instruction, wherein said dependent-process-instruction generating unit is configured to obtain a second process instruction which causes the computer to execute a predetermined process, and to generate the dependent process instruction by converting the second process instruction into the dependent process instruction, and the dependent process instruction causes the computer to derive an execution result identical to an execution result of the second process instruction when a value assigned to the assign-target variable equals a predetermined assumed value, the value assigned to the assign-target variable indicating an execution result of the first process instruction, said instruction generation apparatus further comprising: an obtaining unit configured to obtain an input program which includes: the second process instruction that does not use the first process instruction; and a third process instruction which causes the computer to execute a process different from the second process instruction using the first process instruction; and an output unit configured to output an output program which includes the third process instruction and the output process instruction group, the output process instruction group including the dependent process instruction generated through the conversion of the second process instruction included in the input program by said dependent-process-instruction generating unit.