An impeller of a multiblade fan includes a discoid main plate that rotates about a rotational axis, blades, and a side plate. The blades are disposed annularly about the rotational axis on one side of the main plate, with one end of each of the blades being fixed to an outer peripheral portion of the main plate. The side plate includes an annular side plate body portion that joins outer peripheral edges of the other ends of the blades to each other, an axially extending portion that extends from an opposite-main plate side end of the side plate body portion in the rotational axis direction further than the opposite-main plate side ends of the blades, and a radially extending portion that extends from an outer peripheral end of the side plate body portion further than a radial-direction outer peripheral end of the axially extending portion.