A linear actuator that does not require a high assembly precision is provided. A linear actuator includes a motor portion including a rotary shaft, a rotor, and a stator, a first bearing portion that supports a first end of the rotary shaft, a locknut threadably engaged on the first end of the rotary shaft, and a ball screw mechanism including a ball screw nut screwed to the locknut and a ball screw threadably engaged with the ball screw nut. Gaps formed between an outer peripheral portion of the rotary shaft and an inner peripheral portion of the locknut, except a male thread portion formed on the rotary shaft and a female thread portion formed on the locknut threadably engaged with each other, are defined to have respective predetermined sizes.