Linear actuator, where a reversible electric motor (20) through a transmission (21) drives a non-self-locking spindle (22), by means of which an adjustment element (24) secured against rotation can be moved axially for adjusting an element connected thereto such as a backrest section in a bed. The actuator further comprises a quick release (27) for disengagement of the adjustment element (24) from the electric motor (20) and the part of the transmission (21) extending from the electric motor (20) to the quick release (27), such that the spindle (22) is rotated under the load on the adjustment element (24). Further, the actuator comprises brake means for controlling the speed of the adjustment element (24), when the quick release (27) is activated. The brake means are constituted by a rotary damper (45) of the fluid type comprising an internal body located in a liquid-filled hollow in an outer body, where one body is in driving connection with the spindle (22) or the part of the transmission extending from the spindle (22) to the quick release (27), and where a dampening effect, which dampens the speed of the spindle (22) and thus the adjustment element (24), is generated when this body is rotated relative to the other body as a result of activation of the quick release (27). It is thus possible to provide a construction where the lowering speed is self-controlling when the quick release is activated.