A centrifugal blower having high efficiency and reduced noise is provided. A centrifugal blower to be accommodated in a housing having an air inlet includes a spiral casing having a bell mouth and a centrifugal fan housed in the casing. The bell mouth includes a first region and a second region. The first region is disposed closest to the air inlet. A distance from a rotational axis of the centrifugal fan to a downstream end in the first region is greater than a distance from the rotational axis to the downstream end in the second region. A curvature of a surface of the first region in a cross section including the rotational axis is smaller than a curvature of a surface of the second region in a cross section including the rotational axis.