This invention provides a small-form-factor linear actuator that exhibits low back-drive force. Said linear actuator has a hollow rotor, a main body, a linear-motion conversion part, a linearly moving rod, and a resolver. The rotor has an open end and a closed end, and magnets are affixed to part of the outside surface thereof. The main body has a hollow structure with an open end and a closed end, and the rotor is rotatably accommodated inside said hollow structure. A stator winding is affixed to the main body so as to face the aforementioned magnets. The linear-motion conversion part is disposed in the hollow part of the rotor and moves linearly in an axial direction as a result of rotation of the rotor. One end of the linearly moving rod is affixed to the linear-motion conversion part, and the other end thereof protrudes from the open end of the main body. The linearly moving rod has, on the outside surface thereof, a sliding section that slides axially against a linear-motion seal on the open end of the main body. The resolver comprises a rotor element that is affixed radially outwards of the outside surface of the rotor, at a point that is closer to the open end of the rotor than the closed-end surface of the rotor is, and a stator element that is affixed to the main body within an angular range corresponding to the radially outer part of the rotor element. The rotor is supported on the main body, at the closed end thereof and on the open-end side of the magnets and the stator winding, so as to be able to rotate axially. The entire hollow rotor is accommodated inside a sealed space.