PURPOSE: To improve operability and safety by differentiating the signal from a detecting means of the weight of a load, adding and averaging the weight detection values at one or more middle points from one zero point to the next zero point of the differentiated signal, and using the average value as the memory value of the weight of the load.

CONSTITUTION: A lift system lifting or lowering a load, a lift driving motor 2 driving the lift system, a speed command unit 6 used by a worker to command the speed of the lift system, a speed detector 19 detecting the speed of the lift system, a position detector 21 detecting the position of the lift system, and a load detector 14 detecting the weight of the load are provided. The load detection signal WA from the load detector 14 is differentiated, load detection signals at the middle points from the zero point of the differentiated signal value to the next zero point are added and averaged in a load arithmetic section 16, the average value is stored in a weight memory section 17 as the weight of the load, and these output signals are calculated in an arithmetic section 13 to control the movement of the lift system.