To provide a rotating shaft connecting mechanism ensuring that the elliptical connection of a pressure roll can be pressed into contact by causing an elliptical inner hole in a roll coupling to uniformly contract.

The roll coupling 2 having the elliptical inner hole 2a into which the elliptical connection 1a formed at the axial end of the pressure roll 1 of a rolling machine is inserted has an outer peripheral surface formed with an elliptical cross section concentric with the elliptical inner hole 2a, and a spacer 4 with an arc-shaped cross section is inserted between the planar portion 2c of the outer peripheral surface and the inner peripheral surface of a sleeve 3 with a hydraulic pressure expansion chamber.