PURPOSE: To prevent the occurrence of overheat and the stop of an electric motor and a fear of operation owing to the temporary increase of passengers.

CONSTITUTION: Wattmeters 5 and 6 are connected to the primary side of an induction electric motor for drive and a power detected by the wattmeter 5 and 6 to detect the load of the induction electric motor 1 is inputted to a control device 7. When the power and a continuance time exceed a power value and a continuance time previously stored at the control device 7, the effect is displayed at an entrance and riding-in of passengers is suppressed by a speaker 11.