A storage medium readable by a computer is provided. The storage medium stores a program of instructions executable by the computer to perform a function for protecting a target function. The function includes generating an inserted function, having a function name identical to the function name of the target function, that includes code for a process relating to protection of the target function and a call instruction for calling the target function after this process, and generating a protected executable code on the basis of an object code, in which the function name of a function definition of the target function has been changed to a second function name, and the inserted function.