A linear actuator includes a first tube, a second tube inserted into the first tube to be free to slide, a rod fixed at one end of the rod to the first tube, a rod guide provided on the other end of the rod so as to slide relative to the second tube, a plurality of permanent magnets held by the rod, a holder that is fitted into the second tube and holds a plurality of coils, a first chamber defined between one end of the holder and an end portion of the first tube, and a second chamber defined between the other end of the holder and the rod guide. An insertion hole which connects the first chamber to the second chamber and through which the rod passes is formed in the holder. A connecting groove that connects the first chamber to the second chamber is formed in the second tube to extend in an axial direction.