Abstract: A protective device for a water-pump apparatus includes an upright hollow tubular member which is mounted on a top end of a pump unit of the water-pump apparatus, the interior of the tubular member communicating with an interior of the pump unit. A floating switch actuator is provided movably inside the tubular member and floats inside the tubular member in response to water level therein. The switch actuator is provided with a permanent magnet. A control unit is mounted on an outer surface of the tubular member and is connected electrically to a motor unit of the water-pump apparatus. The control unit includes a magnetically actuated switch which is activated by the switch actuator when the switch actuator is at a predetermined position inside the tubular member. The control unit cuts off power supply to the motor unit when the switch actuator ceases to float inside the tubular member.