Workers can be limited by using a Panasonic SG-D1 key selector switch to switch modes when performing maintenance and program overwrites. Additionally, since the NC contact (b-contact) use direct open operation, the circuit will be reliably shut off by forcibly separating the NC contact, even if they have melted together. Use in combination with the safety door switch with key SG-B2 series to enable hostage control. 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.