A centrifugal blower includes an impeller and a casing having an air intake portion. The air intake portion has a bell mouth lower end portion that includes a downstream end, and a bell mouth inner surface portion that includes a radially inner surface. The shroud has a shroud upper end portion that includes an upstream end, and a shroud inner surface portion that includes a radially inner surface. The bell mouth lower end portion and the shroud upper end portion face each other in the axial direction across a gap. A difference between a diameter smallest in the bell mouth inner surface portion and a diameter smallest in the shroud inner surface portion is equal to or smaller than a thickness of the shroud. A vertical vortex generating mechanism configured to generate a vertical vortex is provided on the bell mouth inner surface portion.