Control Device, Unauthorized Command Detection Method, and Program

The present invention aims to provide a control device that reduces load and can provide early detection of program tampering. A main storage unit 102 stores a main application 107 and illegal command information 108. The main application 107 is an extension program in which target commands, which are at least some of the commands included in a prescribed program, have been converted into extension commands. The illegal command information 108 indicates the target commands. A command monitoring unit 104: compares executed commands, which are commands that have been executed by the CPU 103, and target commands, which are indicated in the illegal command information 108; and determines whether or not an executed command is an illegal command, based on the comparison results.