To restrain an increase in the number of parts and installation manhours, in an air blower for constituting a bell-mouth separately from a blower casing.

This air blower is constituted by dividing the blower casing 10A into a first casing 12 and a second casing 11 by a dividing surface in the driving shaft direction of a motor 15. The bell-mouth 18 engages with the periphery of a suction port by sliding in the direction vertical to the dividing surface, and is sandwiched by the first casing 12 and the second casing 11. A locking part 42 regulating a relative position in the rotational direction of a driving shaft to the first casing 12 of the bell-mouth 18, is arranged between the first casing 12 and the bell-mouth 18. Position regulating parts 32 and 55 assisting engagement with the suction port periphery by regulating a relative position in the driving shaft direction of the second casing 11 to the bell-mouth 18 for regulating a position by the locking part 42, are arranged between the bell-mouth 18 and the second casing 11.