Provided is a linear actuator with a dustproof mechanism capable of surely fulfilling the dustproof function over the entire stroke range. The linear actuator (100) with a dustproof mechanism comprises a ball screw, a moving stage (4) which has a ball screw nut engaging with the ball screw and can linearly reciprocates in the axial direction of the ball screw in correlation with rotation of the ball screw, a housing member (2) so installed as to cover at least the ball screw, openings (27, 28) formed in the housing member (2) along the movement path of the moving stage (4), and dustproof belts (29, 30) disposed in the housing member (2) for closing the openings (27, 28), respectively. The linear actuator (100) can have a high dustproof performance since it is equipped with end plate covers (105a, 105b) for covering the end sides of the housing member (2).