PURPOSE: To provide a ventilator for a vehicle capable of reducing the cost corresponding to an opening part for ventilation of various dimensions and shapes through the combination with the box body having the prescribe dimensions and the shape.

CONSTITUTION: A peripheral edge part of a box-shaped body 1 is fixed to an opening part for ventilation of a vehicle body, and a flexible plate member to close a ventilation part 11 formed on the bottom when the in-cabin pressure is normal and open the ventilation part outward so as to discharge the in-cabin pressure from the ventilation part to the atmosphere is provided. Slidable fitting parts 14, 15 for the box-shaped bodies or to fitting parts 13a, 13b to the opening part are provided at least on one outer wall surface of vertical and right-to-left side wall part 12 of the box-shaped bodies 1, and the slidable fitting parts 14,15 are fitted to slidable fitting bars 14b, 15b of the counterparts 1, 13a, 13b for integration.