PURPOSE: To secure the strength of power transmission system and to prevent sympathetic vibration of a rolling mill by the torsional vibration of a spindle by having the taper by which the diameter of the spindle is gradually reduced in the axial direction of roll from a pinion stand.

CONSTITUTION: In a device with which a roll sfaft for rolling mill, motor 10 and the pinion stand 9 are connected through couplings and the spindles, the tapers by which the diameters of the spindles 5, 6 are reduced toward the roll sfafts from the side of the pinion stand 9 are provided. That is, the longitudinal sections of the spindles 5, 6 are trancated cone shapes. In this way, problems in the strength aspect are reduced by making the diameter on the roll side smaller and making the diameter on the pinion stand side larger, and the diameter of roll is further reduced.