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 dependent 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 dependent 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, and wherein the simulation executing part performs: correcting the execution time of the externally dependent instruction by using a correction value based on a delay time of the externally dependent instruction and an 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 the corrected execution time of the externally dependent instruction as the execution time of the externally dependent instruction, wherein the simulation executing part detects, from the instructions included in the block, an instruction that uses an execution time of an immediately preceding instruction for a calculation of an execution time of the detected instruction, and generates the host code including a host instruction that calculates the execution time of the detected instruction.