A program verification system of the invention includes program verification means 51 for verifying whether a verification target program input as a program operating in a secure environment does not include a program execution function which is a function of executing a new program in the same environment by a command in the corresponding program and/or whether the verification target program or a protection mechanism of the secure environment as an operation source of the verification target program includes an external input attack defense function which is a function of defending against an attack caused by an external data input during execution of the program; and signature means 52 for giving a signature to the program based on a result of the verification by the program verification means 51.