To provide a speed-changing rolling method of an Assel mill to minimize hindrance of productivity during seamless steel pipe elongator rolling.

In this speed-changing method of an Assel mill, when the number of revolutions of rolls is controlled during seamless steel pipe elongator rolling, the number of revolutions during rolling is reduced only for the rear end portion of a shell so as to restrain deflection of the product and obtain a product equivalent in thickness deviation accuracy of the rear end portion to the product rolled at the reduced number of revolution.