A method for manufacturing a turbo fan unit includes a step for preparing multiple fan blades and an other-side side plate, and a step for connecting each of the multiple fan blades to the other-side side plate by a welding process. In the preparing step, one of the fan blade and the side plate is prepared, in which a connecting-surface forming portion having a connecting surface and a welding projection protruded from the connecting surface is formed. The connecting surface connects one of the fan blade and the side plate to the other one of the fan blade and the side plate. In the connecting step, the welding projection is melted down and the connecting surface is connected to an opposing surface, which is the surface of one of the fan blade and the side plate and which is opposing to the connecting surface.