To solve the problem of generation of deflection in hook positions in spite of synchronized operation due to difference between two hoists such as diameter difference between their rope winding drums, initial elongation difference between their ropes, etc.

The hooks of the two hoists are positioned to the same position around the upper limit of a hook action range, and pulse count numbers of both are set at the same value. Correction coefficients are computed based on the pulse count numbers in accordance with lower reference points set close to the lower limit in the hook action range, and the pulse count numbers interlocked with the hook positions are corrected to be used for hook position control.