There is provided a centrifugal air blower that can reduce driving force (consumed driving force) when an air blower is rotated, and also increase an airflow amount of air to be blown out from the air blower. A centrifugal air blower having an impeller 1 comprising a main plate 3 and plural vanes 2, and a side plate having a suction port and a blow-out port is characterized in that when the height of the suction port is represented by H, the height of the blow-out port is represented by h, the diameter of the impeller is represented by D and the diameter of the suction port is represented by d, 0.5