To provide a ventilating device for an incoming facility allowing safe maintenance and exchanging work of a ventilating fan from the outside of a casing regardless of structure of a casing, while requiring a small extrusion size of a hood.

The ventilating device comprises the hood 10 covering the outer face of a vent hole 9 opened in the peripheral wall of the casing 1, and the ventilating fan 11 arranged inside the hood 10 for forcibly ventilating air in the casing 1. The hood 10 has a hood body 14 covering the outer face of the vent hole 9, a fastening frame 15 joined to the peripheral edge wall of the vent hole 9, and a mounting frame 16 fixed to the inner face of the hood body 14 in forward tilting attitude. A downward vent hole 20 is opened in the lower face of the hood 10. The ventilating fan 11 is detachably fastened and fixed to the mounting frame 16 through the vent hole 20. The mounting frame 16 forward tilts in upward inclination ranging from around the lower edge of the vent hole 9 upward to the front side. The rotational plane of the ventilating fan 11 has an inclination θ of 45°.