A linear actuator (1) having: a shaft (26) that is forward/reverse rotated by a motor via a worm (36) and a worm wheel (41) a screw nut (29) threadably mounted to the shaft (26) and a piston tube (10) fixed to the screw nut (29) and that advances and retreats in accordance with the rotation of the shaft (26). A metal coupling (42) is attached on the inside, in the radial direction, of the worm wheel (41). A one-way clutch (44) is attached on the inside, in the radial direction, of the coupling (42). A brake unit (45) that does not apply braking force during forward rotation, during which the piston tube (10) extends, and does apply braking force during reverse rotation of the piston tube (10) is connected to the one-way clutch (44).
