A ventilation unit (1A) is equipped with: a ventilation member (2) that is attached to an aperture (11) of a chassis (10) and includes a waterproof ventilation film (4) for covering the aperture (11); a sealing member (6) that seals the gap between the chassis (10) and the ventilation member (2); and a ring-shaped partition wall member (7A), in the interior of which the ventilation member (2) is inserted. The partition wall member (7A) is formed so as to be capable of being held while in contact with the chassis (10), and covers the gap formed between the chassis (10) and the peripheral part of the ventilation member (2) outside of the sealing member (6) when the ventilation member (2) is attached to the aperture (11) of the chassis (10).
