A multi-blade fan including a spirally-shaped casing having an inlet and an outlet; an electric motor disposed inside the casing; a main plate provided perpendicular to a rotation axis of the electric motor and having a ventilation hole; first blades disposed at a side of the inlet of the main plate; and second blades disposed at an opposite side of the inlet of the main plate. Herein, a diameter of the main plate is smaller than an outer diameter of the first and second blades and is larger than an inner diameter of them. Furthermore, an outlet angle of any one or both of the first blade and the second blade is sequentially changed in an axis direction.