A position unit is mounted on an electronic device and includes a catch member and a locking member. The catch member defines a gap which has a width that is reducible when the catch member moves from a non-catching position to a catching position and that is expandable when the catch member moves from the catching position to the non-catching position. The locking member has an engine end extending into the gap. The locking member is operable to move the catch member from the non-catching position to the catching position and from the catching position to an urging position. The engaging end of the locking member engages the catch member when the width of the gap is reduced upon movement of the catch member to the catching position. The engaging end of the locking member disengages from the catch member when the width of the gap is enlarged upon movement of the catch member to the non-catching position.