PURPOSE: To regulate nip pressure automatically by installing a control part for controlling a driving means so as to drive a shaft center movable roller in the nip pressure relieving direction at a time when the detected value of a speed measuring means is less than the reference speed.

CONSTITUTION: In this device, there are provided a speed measuring means 29, detecting rotational speed of either of a shaft center fixed side roller 1 or a shaft center movable side roller 3, a speed setting means 33, setting a reference speed of the roller 1 on one side, and a control part 37 controlling a driving means of a shaft center mobile mechanism on the basis of comparison between the reference speed and the rotational speed detected by the speed measuring means 29. At this time, the control part 37 controls the driving means 17 so as to drive the shaft center movable roller 3 in the pressure-contact direction when the rotational speed detected by the speed measuring means 29 exceeds the reference speed, and in the pressure-contact relieving direction when the detected value of the speed measuring means 29 is less than that reference speed, respectively.