PURPOSE: To enable an accurate weighing of an article to be transported by detecting variation in the power consumption based on the rise in the temperature of a motor or the like to correct the variation in the weight of the article with changes in the power consumption of the motor in the driving to hoist.

CONSTITUTION: 3-phase AC power lines 6aW6c, current transformers 7a and 7b and a transformer 8 are connected to a motor 5 of a crane 1. Then, a weight measuring device 2 comprising a power converter 9, an analog arithmetic unit 10, an A/D converter AD, a processor CPU and a display 11 is provided. The weight measuring device 2 computes the variation ΔP in the power consumption of the motor 5 from the power consumption PD when an empty backet 3 premeasured is hoisted down and the read power consumption PD' to calculate the weight ΔW to be corrected while the polarity is determined. Then, the weight W of the article being transported is calculated from the power consumption PL of the motor 5 when the backet 3 grabbing it 4 is hoisted up and the weight correction value ΔW.