A centrifugal fan comprising: a rotatable impeller; and a fan housing in which the impeller is disposed, the fan housing having first and second inlets (122h; 124h) intaking air along a rotation axis of the impeller and an outlet exhausting air in a direction perpendicular to the rotation axis, wherein the fan housing comprises: a first plate having the first inlet; a second plate forming a space with the first plate to accommodate the impeller, the second plate having the second inlet; and a sidewall connecting the first plate to the second plate, the sidewall expanding at an outer side of the impeller in a circumferential direction to guide air flowed through the first and second inlets (122h, 124h) to the outlet, wherein the impeller comprises: a main plate having a first side facing the first inlet and a second side facing the second inlet; a plurality of first blades arranged on the first side in a circumferential direction; and a plurality of second blades arranged on the second side in a circumferential direction, wherein the sidewall comprises: a first convex part protruding away from the rotation axis, the first convex part expanding outside the first blades in a circumferential direction; and a second convex part protruding away from the rotation axis, the second convex part expanding outside the second blades in a circumferential direction, wherein: the sidewall comprises a curved section wound in a circumferential direction to have a scroll shape, the first convex part and the second convex part are formed at the curved section, and the first convex part and the second convex part are connected to each other, the first convex part and the second convex part forming a "W" shape, characterized in that a first space between the first blades and the first convex part and a second space between the second blades and the second convex part are not separated from each other. a rotatable impeller; and a fan housing in which the impeller is disposed, the fan housing having first and second inlets (122h; 124h) intaking air along a rotation axis of the impeller and an outlet exhausting air in a direction perpendicular to the rotation axis, wherein the fan housing comprises: a first plate having the first inlet; a second plate forming a space with the first plate to accommodate the impeller, the second plate having the second inlet; and a sidewall connecting the first plate to the second plate, the sidewall expanding at an outer side of the impeller in a circumferential direction to guide air flowed through the first and second inlets (122h, 124h) to the outlet, a first plate having the first inlet; a second plate forming a space with the first plate to accommodate the impeller, the second plate having the second inlet; and a sidewall connecting the first plate to the second plate, the sidewall expanding at an outer side of the impeller in a circumferential direction to guide air flowed through the first and second inlets (122h, 124h) to the outlet, wherein the impeller comprises: a main plate having a first side facing the first inlet and a second side facing the second inlet; a plurality of first blades arranged on the first side in a circumferential direction; and a plurality of second blades arranged on the second side in a circumferential direction, a main plate having a first side facing the first inlet and a second side facing the second inlet; a plurality of first blades arranged on the first side in a circumferential direction; and a plurality of second blades arranged on the second side in a circumferential direction, wherein the sidewall comprises: a first convex part protruding away from the rotation axis, the first convex part expanding outside the first blades in a circumferential direction; and a second convex part protruding away from the rotation axis, the second convex part expanding outside the second blades in a circumferential direction, wherein: a first convex part protruding away from the rotation axis, the first convex part expanding outside the first blades in a circumferential direction; and a second convex part protruding away from the rotation axis, the second convex part expanding outside the second blades in a circumferential direction, wherein: the sidewall comprises a curved section wound in a circumferential direction to have a scroll shape, the first convex part and the second convex part are formed at the curved section, and the first convex part and the second convex part are connected to each other, the first convex part and the second convex part forming a "W" shape, characterized in that a first space between the first blades and the first convex part and a second space between the second blades and the second convex part are not separated from each other.