Centrifugal blower and air conditioning device

A centrifugal blower (1) is provided with: a fan (2) having a disc-shaped main plate (2a), a plurality of blades (2d), and an annular side plate (2c) to which the ends of the plurality of blades are fixed; and a volute (4) having a peripheral wall (40) formed in a vortex shape and at least one side wall (4a) having a bell mouth (3) forming a suction port (5), forming a discharge port (42a) and housing the fan, the volute having a tongue portion (43) and a plate-shaped extension plate (45) extending from the tongue portion along the outer peripheral edge of the fan in a state of being spaced apart from the fan, the extension plate is formed such that a portion on the side plate side is longer than a portion on the main plate side, and has a tail end portion (46a) which is a tail end portion of the extension plate in a protruding direction from the tongue portion and is located at a boundary portion with the at least one side wall, and which is configured so that when the volute is projected in the axial direct