An actuator device for actuating linear displacement, comprising: - a main rod; - a first chamber housing a substance such that its specific volume changes in the event of temperature changes, the first chamber being configured to be in thermal contact with a heat source; - an inner rod emerging from the first chamber and movable in an axial direction (X-X') to apply a drive force in response to the variation in the volume of the substance housed in the first chamber; - a first base adapted for being impelled by the inner rod and movable in the axial direction (X-X'), wherein the main rod is movable in the axial direction (X-X') and is attached to a second base either at an end or close to an end, wherein said second base is movable in the axial direction (X-X'); - an inner support surface (8.1) attached to the first base by means of a spacer element separating it according to the axial direction (X-X') from said first base, wherein the inner support surface (8.1) limits the movement of the second base; - a first spring with a first elastic constant located with one end supported on the first base and the opposite end supported on the second base, such that the second base can be moved closer to the first base by means of compressing the first spring; - an outer shell attached to the first chamber and housing the assembly formed by the first base and the inner support surface (8.1), as well as the second base, wherein it additionally houses a second spring with a second elastic constant, and wherein: the second spring is located with an end supported on the first base and the opposite end supported on the outer shell, such that the first base is movable under compression of the second spring to recover the position of the first base when the inner rod no longer applies any force characterised in that the outer shell is closed by a seating (9.5) guiding the axial movement (X-X') of the main rod. - a main rod; - a first chamber housing a substance such that its specific volume changes in the event of temperature changes, the first chamber being configured to be in thermal contact with a heat source; - an inner rod emerging from the first chamber and movable in an axial direction (X-X') to apply a drive force in response to the variation in the volume of the substance housed in the first chamber; - a first base adapted for being impelled by the inner rod and movable in the axial direction (X-X'), wherein the main rod is movable in the axial direction (X-X') and is attached to a second base either at an end or close to an end, wherein said second base is movable in the axial direction (X-X'); - an inner support surface (8.1) attached to the first base by means of a spacer element separating it according to the axial direction (X-X') from said first base, wherein the inner support surface (8.1) limits the movement of the second base; - a first spring with a first elastic constant located with one end supported on the first base and the opposite end supported on the second base, such that the second base can be moved closer to the first base by means of compressing the first spring; - an outer shell attached to the first chamber and housing the assembly formed by the first base and the inner support surface (8.1), as well as the second base, wherein it additionally houses a second spring with a second elastic constant, and wherein: the second spring is located with an end supported on the first base and the opposite end supported on the outer shell, such that the first base is movable under compression of the second spring to recover the position of the first base when the inner rod no longer applies any force characterised in that the outer shell is closed by a seating (9.5) guiding the axial movement (X-X') of the main rod. the second spring is located with an end supported on the first base and the opposite end supported on the outer shell, such that the first base is movable under compression of the second spring to recover the position of the first base when the inner rod no longer applies any force characterised in that the outer shell is closed by a seating (9.5) guiding the axial movement (X-X') of the main rod.