In the present invention, an outer peripheral surface (14S) of a second bell mouth (14) is located in a lower side (V) in a vertical direction of a lower end (16) of a first bell mouth (12). That is, the lower end (16) of the first bell mouth (12) is located opposite to a direction (D2) in which the second bell mouth (14) is opened, compared to an upper end (18) of the second bell mouth (14) in the lower side (V) in the vertical direction of the lower end. In other words, the upper end (18) of the second bell mouth (14) in the lower side (V) in the vertical direction of the lower end (16) of the first bell mouth (12) is located closer to the direction (D2) in which the second bell mouth (14) is opened, than the lower end (16).