There is provided a linear actuator provided with a dust-proof mechanism capable of preventing dust-proof belts from being deformed, improving a sealing performance between the dust-proof belts and a housing member, and achieving high dust-proof performance irrespective of a size of the linear actuator. The linear actuator provided with the dust-proof mechanism includes: a housing member disposed so as to cover at least a ball screw; an opening portion formed in the housing member so as to extend along a moving locus of a movable stage; and dust-proof belts stretched inside the housing member so as to close the opening portion by being mounted to mounting members disposed both end portions of the housing member, wherein a bypass member for bypassing the dust-proof belts positioned at position overlapped with the movable stage is provided for the movable stage so as to realize movement of the movable member along the opening portion while closing and sealing the opening portion by the dust-proof belts, and in such a linear actuator provided with the dust-proof mechanism, the dust-proof belts are wound up around the mounting member and sandwiched between the mounting member and the end portions of the housing member.