A linear actuator for a piece of furniture, namely a bed or chair comprising a housing (8) of plastic consisting of two parts (8a, 8b) with a joining edge (8c) in the longitudinal direction of the housing. In both ends of the housing there is a transverse through aperture (10) for receiving a pivot shaft in the piece of furniture, and with an openable cover (9) for mounting the actuator on the shafts. In connection with the apertures there is a drive comprising a reversible motor, which over a transmission drives a spindle, and where a spindle nut fixed against rotation and constructed as a sliding element is mounted on said spindle. The pivot shaft in the piece of furniture has an arm which rests loosely against the end of the spindle nut when the actuator is mounted on the piece of furniture so that the pivot shaft is rotated for raising of a section in the piece of furniture in one direction of movement of the spindle and for lowering the section under its weight in the other direction. The two parts of the housing (11a, 11b) are join together by gluing or welding, which simplifies the mounting and shape of the housing compared to the traditional assembly with screws.