A program execution control apparatus and a program execution method are provided by which even when a program is rewritten into an illegal program after the first-mentioned program is checked, execution of the rewritten illegal program can be avoided, and also, which can readily confirm that which program has been rewritten in an illegal manner at which time instant.The program execution control apparatus of the present invention is equipped with: a flash memory 101 for storing thereinto a program; a condition detection unit 103 for detecting a check time instant for checking as to whether or not the program is illegal; an illegality check unit 104 for checking as to whether or not the illegal program is present at the check time instant; an execution control unit 105 for controlling as to whether or not the program is executed in response to the check result; and a CPU 102 for executing the program in response to a result of the execution control unit 105.