Control device, security management system, and security management method

A central processing unit 3 of a control device includes: a control calculation unit 32 that performs calculation on the basis of storage content of a nonvolatile storage unit 31 and controls a machine; an update unit 33 that accepts operation input in a first maintenance mode or a second maintenance mode, which has a narrower operable range than the first maintenance mode, and updates the storage content of the nonvolatile storage unit 31 in accordance with the operation input; a security management unit 34A that determines permission or prohibition of the operation input in the first maintenance mode with the use of a hardware key 6; and a security management unit 34B that determines permission or prohibition of the operation input in the second maintenance mode without the use of the hardware key 6.