1. A simulation apparatus comprising: a code converting part; and a simulation executing part, wherein the code converting part performs: dividing code of a program in a target processor which is controlled by a host processor into blocks; setting an execution result of an externally dependant instruction depending on an external environment included in a block as a prediction result; carrying out function simulation based on the prediction result; calculating an execution time of the externally dependant instruction under the prediction result according to instruction execution timing information included in the block and a function simulation result; and generating host code which makes the host processor execute performance simulation under the prediction result based on the function simulation result, wherein the simulation executing part performs: correcting the execution time of the externally dependant instruction by using a correction value based on a delay time of the externally dependent instruction and a execution time of an instruction executed before or after the externally dependent function if an execution result of the externally dependent function when the host processor executes the host code differs from the prediction result; and setting a corrected execution time of the external dependent instruction as the execution time of the externally dependant instruction.