A ventilation structure (10A) includes a housing (50) having an opening portion (50a) and a ventilation member (1A) formed of a porous resin and attached to the housing (50) so as to cover the opening portion (50a). In the ventilation structure (10A), the ventilation member (1A) is fitted to a side surface (50d) of a projecting portion (50b) provided on an outer surface of a wall portion (50g) of the housing (50), with at least one of the projecting portion (50b) and the ventilation member (1A) being elastically deformed.