PURPOSE: To provide a blowoff opening structure wherein a guarantee of a more stable operation performance or a stable holding of a damper in a time of an air-conditioned air blowing can be contrived, and, besides, a wider ventilation area can be ensured and an appearance can be raised.

CONSTITUTION: Dampers 12, 13 executing opening or shutting of a blowoff opening 10a are set at cylindrical cases 4, 5 forming an air ventilation path 10, and a rod material 15 which can reciprocate along a longitudinal shaft direction between the dampers, and can be locked in a predetermined reciprocating position by a locking mechanism. Besides, gears 22, 23 executing opening or shutting of respective dampers to the accompaniment of the reciprocating motion of a lack gear tooth 15a and an engagement rod member are mounted on a rotating shaft 12s of respective dampers, the rod member is reciprocatably supported at two places of front and back, that is to say, at a front side and a back side of an engagement section with a gear, and further, a lock means is set at a supporting section at a back side of the rod member.