Autofocus device including line image forming unit and rotation unit that rotates line image

An autofocus device comprising:

• an optical source;
• an optical unit that allows emitted light from the optical source and object light from a measurement target to pass through the same optical path, the optical unit being arranged between the optical source and the measurement target;
• and
• a detection unit that performs focus detection by using the object light passed through the optical unit,
• wherein the optical unit comprises:
• a tube lens that forms the emitted light into parallel light;
• an image forming unit that forms a continuous line image on a surface of the measurement target by the parallel light from the tube lens;
• and
• a rotation unit that rotates the continuous line image around an axis of the optical path between the optical unit and the measurement target.