To temporarily operate a motor by preventing a complete stop of an inverter during regenerative operation of the motor by a conventional circuit, to notify the outside of a state that a regenerative resistor is disconnected, and to execute frequency control in order to prevent an inverter stop.

A regenerative resistor is used to consume regenerative power from a motor. A regenerative-resistor failure judgement circuit is composed by combining a plurality of regenerative resistors arranged in parallel and a current detector for detecting a regenerative current value flowing in the regenerative resistors. It is configured to use a method that judges step by step the number of disconnected resistors corresponding to current changes by catching changes in regenerative current value by the circuit. It is also configured to provide a means that executes control for lowering a frequency of a frequency converter by capturing information obtained from the circuit with a control part for executing frequency control. It is devised to prevent a stop of an electric winch by using the method and the means. It is also devised to obtain a means for notifying the outside by combining the control part with a display device, a speaker device, and a vibration generator or the like.