A centrifugal blower has a scroll casing, and a separation cylinder. The scroll casing has a nose portion having a minimum scroll diameter and a scroll end portion having a maximum scroll diameter. A suction port of the scroll casing is divided into a first half region and a second half region by a reference line passing through a rotation axis and the nose portion. An air introduction portion of the separation cylinder is arranged to have an area overlapping the first half region in the axial direction, which is larger than an area overlapping the second half region. An outer peripheral wall of the scroll casing is set such that a divergence angle from the nose portion to an intermediate portion is larger than a divergence angle from the intermediate portion to the scroll end portion.