A joining device includes a first holding unit configured to load and hold the first member on its top surface; a second holding unit disposed above the first holding unit while facing the first holding unit and configured to hold the second member; and a position adjustment mechanism configured to adjust a joining position between the first member held by the first holding unit and the second member held by the second holding unit. The second holding unit is of a circular plate shape, and the position adjustment mechanism includes four position-adjusting cam members disposed at equal intervals along an outer peripheral surface of the second holding unit, and moves the second holding unit in a horizontal direction.