It is intended to provide a centrifugal blower capable of suppressing the generation of noise including periodic noise that is caused by interference between a tongue and an impeller. The centrifugal blower is provided with an impeller (2) provided with plural blades around a rotating shaft; a casing (3) which houses the impeller (2) and has a suction portion at one end in an axial line direction of the rotating shaft; a spiral flow passage (4) formed around the impeller (2) in the casing (3); and a tongue (6) for suppressing inflow of air from a winding end to a winding origin of the spiral flow passage (4). The centrifugal blower is characterized in that an extension (20) is provided at a tip of the tongue (6) in a reverse rotational direction that is reverse to a rotational direction of the impeller (2) in such a manner that it projects in the reverse rotational direction by a length that varies depending on the position in the axial line direction and that the gap between itself and the impeller (2) in the radial direction of the impeller (2) is kept approximately constant.