PURPOSE: To enable sure mounting without causing any clatter and make mounting and dismounting easy by pressing the inside circumferential surface of the die by pressure fluid to expand its inside diameter thereby mounting the die to the spindle.

CONSTITUTION: In the case of mounting a die 2 to a rolling spindle 1, the inside diameter of the die 2 is made slightly smaller than the outside diameter of the spindle 1 to provide an interference. Because of this, the die is not perfectly fitted up to the stopper 8 of the spindle 1 and contacts the outside circumferential part of the taper just before the same. When in this state pressure fluid is led into grooves 6 for pressure fluid through pressure fluid lead-in holes 7, the die 2 slightly expands toward the outside circumferential direction and produces a spacing between the same and the outside circumference of the rolling spindle. The die 2 is pulled by pull bolts 3 to let the die contact the stopper 8. When the pressure fluid is released after this, the die 2 contracts in the inside diameter direction and is firmly fixed to the outside circumference of the spindle in the state of interference fit by leaving an interference. To remove the die 2 from the spindle 1, the pressure fluid is led in to produce a spacing and the pull bolts 3 are loosened, thence the die 2 is pushed out by push-out bolts 4.