PURPOSE: To simplify construction of a centrifugal blower by extending a mirror plate constituting a side face of the casing, by giving the outside configuration a rectangular form to incorporate an electric motor, and by furnishing a driver device for a wind quantity control member inside this casing.

CONSTITUTION: A mirror plate 3 constituting a side face of the casing 1 is extended, and the outside configuration of the blower is given a rectangular form. An electric motor 6 to drive an impeller 5 is built in this rectangular body, being located in the space formed between the discharge part 4 of the casing 1 and the wind starting part 2a' of the circumferential plate 2 constituting said casing 1. In this casing 1 is also furnished a driver device for a wind quantity control member, so that the overall construction can be simplified.