A linear actuator with a dust-proof mechanism reliably protects the actuator against dust in the entire stroke range of the actuator. The linear actuator preferably has any one of the following structures: a suction opening is provided at an end of a housing member (2); suction openings are arranged at side surfaces of the housing member (2) such that more number of suction openings of the suction openings are arranged on opposite end sides of the housing member (2) than at the center thereof; a partition wall (111) is formed inside the housing member (2) to partition the inside of the housing member (2) into a movement section (a) for a movement stage (4) and a flow section (ß) for sucked air; and a flow section (ß) is formed on the bottom surface side of the housing member (2) by utilizing a cavity formed when the housing member (2) is formed by extrusion. The partition wall (111) has openings (112), and preferably, the suction openings and the openings (112) are faced to each other.
