The safety door switch with key Panasonic SG-B2 series locks and unlocks doors with keys. When an operator takes a key into a hazardous area, the safety door switch will not lock, and the equipment will stop, ensuring operator safety by preventing personnel from being closed inside the hazardous area and preventing equipment from starting to operate. Hazards of the system and robot are isolated by the safety guard. The worker uses the key to unlock the door and disables the system from starting unexpectedly, then removes the key and brings it into the hazardous area. The system remains off until the worker walks out the door and locks the door with the key. This enables the worker carrying the key to work safely in the hazardous area. Hazards of the system and robot are isolated by the safety guard. When a worker needs to work inside the hazardous area for maintenance, the worker unlocks the safety guard using a key, disables the system from starting (1), removes the key and brings it into the hazardous area, and then changes the operation mode of each system to maintenance mode (2). While the worker is carrying out maintenance work in the hazardous area, the safety guard cannot be locked and the system cannot be turned on. This enables the worker to work safely in the hazardous area.