A centrifugal fan mounted in an air conditioner has the following relationship: outer diameter of a side plate of the centrifugal fan>outer diameter of the blade rear-edge part on side-plate side>diameter of the blade rear-edge part on main plate side>outer diameter of the main plate. In the centrifugal fan, the blade rear-edge part is positioned inside from a straight line connecting the connection point between the blade rear-edge part and the main plate, to the connection point between the blade rear-edge part and the side plate, as viewed from the rotation axis. The blade rear-edge part has a shape such that the distance from the rotation axis becomes larger from the main plate toward the side plate.