To detect and protect an abnormal temperature rise in a coil by providing thermosensitive devices on a coil outer periphery of motors, taking signals of the thermosensitive devices in a control device, and stopping operational indication to the motors when the signals of the thermosensitive devices are judged as an OFF signal.

Thermosensitive devices 24(a) and 24(b) are provided on a coil outer periphery of motors 25 and 26, and are connected to a control device 29 through signal conductors 27 and 28. The control device 29 and speed control devices 32 and 33 are connected to each other through signal conductors 30 and 31. When a contact point of the thermosensitive device 24(a) opens since a coil of the motor 25 abnormally rises in the temperature by long hour continuous operation of a pump and a rare short circuit of the coil or the like, the control device 29 judges it as an OFF signal through the signal conductor 27, and stops operational indication to the speed control device 32 through the signal conductor 30. The speed control device 32 receives information of the control device 29, and stops the motor 25 to cut off output to the motor 25. Therefore, an abnormal temperature rise in the coil is detected, and this can be protected.