Abstract: An actuator (10a, 10b) for calender rolls (3, 4) in a machine calender connected on-line to a paper machine, wherein the actuator is situated between the calender frame (9) and support arms (11), which adjust the movable calender rolls (3,4), in order to load and unload the nips (N.sub.3, N.sub.2) formed by the calender roll (3, 4) in question and its counter roll (3, 2), and to lock the calender rolls (3, 4) to the top position (3', 4'). The actuator (10a, 10b) is of modular construction and consists of a movable frame (13), which forms the frame of the actuator, and which can be connected to the vertical side (9c) of the claender girders (9) so that the vertical position of the movable frame (13) can be adjusted. The actuator module is equipped with a double acting hydraulic cylinder (12), which is connected between the movable frame (13) and the support arms ( 11) of the calender rolls (3, 4) to load and unload the calender nips and to lift the rolls (3, 4) to the top position.