A device for adjusting a press nip (126) defined by a first press roll (102) and a second press roll (104), each press roll being rotatable about an axis of rotation (103, 105) and included in an apparatus for dewatering pulp, and the apparatus has a first pair of bearing housings (220) provided with bearings (218) by means of which the first press roll is journalled, each bearing housing of the first pair and the first press roll being movable in relation to the second press roll in a direction substantially transverse to the axial direction of the press nip, the device comprising pressure means (222) for forcing the bearing housings of the first pair in a direction towards the press nip, the first press roll being movable between a first radial end position and a second radial end position. The device is arranged to adjust the press nip during operation of the apparatus and comprises at least one adjusting cylinder (223; 402) for adjusting the first press roll to each of the radial end positions during operation of the apparatus, the adjusting cylinder being arranged to force at least one of the bearing housings of the first pair in a direction away from the press nip to move the first press roll to one of the radial end positions, and the adjusting cylinder has a length of stroke (S) that defines the difference between two different press nips (I, II) for the apparatus, wherein the length of stroke (S) of the adjusting cylinder (223; 402) is adjustable to adjust the difference between the two different press nips (I, II). An apparatus for dewatering pulp comprises such a device for adjusting the press nip.