A linear actuator includes a housing formed of a first half shell and a second half shell and defining an accommodation chamber, a front opening in front of the accommodation chamber and a receiving chamber at the bottom side of the accommodation chamber, a driving mechanism having a push rod movably mounted in the accommodation chamber and extending out of the front opening, a motor mounted outside the accommodation chamber and a spindle coupled to and rotatable by the motor for causing the transmission shaft to reciprocate, and limit switches detachably mounted in the receiving chamber for stopping the motor upon movement of the transmission shaft to a front or rear limit position.