PURPOSE: To detect at least one of a riding car and a balance weight dislocated from a guide rail by deciding a fluctuation width of a lift speed for whether exceeding a prescribed value or not based on a lift speed signal.

CONSTITUTION: A lift speed of a riding car 5 is detected by a lift speed detecting means, to decide whether a fluctuation width of this lift speed exceeds or not a predetermined prescribed value by a speed fluctuation decision means. For instance, at abnormality time of dislocating at least one of the riding car 5 and a balance weight 6 from a guide rail 7, since a fluctuation width of the lift speed is increased as compared with at normal time, here is decided the riding car 5 or the balance weight 6 dislocated from the guide rail 7. Thus by eliminating necessity for a conductive wire and conductive ring, at least one of the riding car 5 and the balance weight 6 can be detected to be dislocated from the guide rail 7.