a scroll casing having an inlet port;

a fan assembly rotatably disposed in the scroll casing;

a motor having a shaft coupled to the fan assembly; and

a bell mouth disposed in the inlet port,

wherein an inner end of the scroll casing, which defines the inlet port, is disposed to be spaced apart from the fan assembly in a radial direction to define a separation space,

wherein an outer end of the bell mouth is disposed to overlap the inner end of the scroll casing in an axial direction to prevent air, which flows by a rotation of the fan, from flowing reversely to the outside of the scroll casing through the separation space,

wherein the bell mouth comprises a band part having an annular shape, and legs protruding from a lower portion of the band part and coupled to the motor,

wherein the band part comprises a body, an inner wheel portion protruding upward from an inner end of the body, and an outer wheel portion protruding upward from an outer end of the body,

wherein the scroll casing further comprises a first protruding portion protruding upward from the inner end of the scroll casing and a guide protruding downward from the inner end of the scroll casing,

wherein the end surface of the outer wheel portion, which is in contact with a lower surface of the inner end of the scroll casing, overlaps with the first protruding portion in the axial direction to guide the flow of air moving toward the inner end upward, and

wherein the guide supports one side of the outer wheel portion.