A safety system comprising: an on-ship system (20, 20a, 20b) that is provided on a ship; and a land system that is provided on land, wherein the on-ship system (20, 20a, 20b) includes a safety detection device and a safety maintenance device for preventing disasters occurring in the ship, that are provided on the ship, a first acquisition unit (25a, 25b) that acquires information detected by the safety detection device and information indicating an operation state of the safety maintenance device, a first control unit (23a, 23b) that controls an actuator included in the safety maintenance device, and a communication unit (26a, 26) that communicates with the land system, and the land system includes a second acquisition unit that acquires the information detected by the safety detection device and the information indicating the operation state of the safety maintenance device through the communication unit (26a, 26), and a second control unit that outputs a control signal for controlling the actuator included in the safety maintenance device to the safety maintenance device through the communication unit (26a, 26), characterized in that after the first control unit (23a, 23b) outputs a control signal to one of the safety maintenance devices, even when the second control unit outputs a control signal to the corresponding safety maintenance device, the control signal is set to be invalid, wherein after the first control unit (23a, 23b) outputs the control signal to one of the safety maintenance devices, when predetermined time elapses or the information detected by the safety detection device is changed, the control signal output to the corresponding safety maintenance device by the second control unit is set to be valid. an on-ship system (20, 20a, 20b) that is provided on a ship; and a land system that is provided on land, wherein the on-ship system (20, 20a, 20b) includes a safety detection device and a safety maintenance device for preventing disasters occurring in the ship, that are provided on the ship, a first acquisition unit (25a, 25b) that acquires information detected by the safety detection device and information indicating an operation state of the safety maintenance device, a first control unit (23a, 23b) that controls an actuator included in the safety maintenance device, and a communication unit (26a, 26) that communicates with the land system, and a safety detection device and a safety maintenance device for preventing disasters occurring in the ship, that are provided on the ship, a first acquisition unit (25a, 25b) that acquires information detected by the safety detection device and information indicating an operation state of the safety maintenance device, a first control unit (23a, 23b) that controls an actuator included in the safety maintenance device, and a communication unit (26a, 26) that communicates with the land system, and the land system includes a second acquisition unit that acquires the information detected by the safety detection device and the information indicating the operation state of the safety maintenance device through the communication unit (26a, 26), and a second control unit that outputs a control signal for controlling the actuator included in the safety maintenance device to the safety maintenance device through the communication unit (26a, 26), a second acquisition unit that acquires the information detected by the safety detection device and the information indicating the operation state of the safety maintenance device through the communication unit (26a, 26), and a second control unit that outputs a control signal for controlling the actuator included in the safety maintenance device to the safety maintenance device through the communication unit (26a, 26), characterized in that after the first control unit (23a, 23b) outputs a control signal to one of the safety maintenance devices, even when the second control unit outputs a control signal to the corresponding safety maintenance device, the control signal is set to be invalid, wherein after the first control unit (23a, 23b) outputs the control signal to one of the safety maintenance devices, when predetermined time elapses or the information detected by the safety detection device is changed, the control signal output to the corresponding safety maintenance device by the second control unit is set to be valid.