To provide: an actuator capable of reducing attaching man-hours, and attachable to a lamp unit having various kinds of design and layout; and an optical axis adjustment device of a vehicular lamp unit using the actuator.

The actuator includes: a first actuator equipped with a first rod, a first actuator body having a first rod projecting opening, including the first rod with at least part projected from the first rod projecting opening, and changing a projecting amount of the first rod, and a first fixation part; a second actuator equipped with a second rod, a second actuator body having a second rod projecting opening, including the second rod with at least part projected from the second rod projecting opening, and changing a projecting amount of the second rod, and a second fixation part; and a connection means relatively rotatably connecting the first actuator to the second actuator.