According to an example embodiment, a firmware rewriting apparatus includes: call position specifying means for specifying, among instructions described in a program of firmware stored in a memory, the instructions for changing a control flow; free area specifying means for specifying a free area in a storage area of the memory in which the program is not stored; and program rewriting means for rewriting the instruction specified by the call position specifying means into a call instruction of a frequency adjustment code and writing the frequency adjustment code for calling an inspection code at a frequency corresponding to a frequency of calling the frequency adjustment code and the inspection code for performing a security check of the program in response to a call from the frequency adjustment code into the free area specified by the free area specifying means.