To materialize a centrifugal fan which satisfies a demand for improvement of a countermeasure against heat dissipation and of implementing under a hostile environment or the like, and also miniaturization and high performance.

In the centrifugal fan, a front casing of a motor also serves as a plate on one side in a cochlear-shaped casing. Or, the front and rear casings in the motor are respectively disposed concentrically on an inner peripheral side and an outer peripheral side connected thereto to form a plate on one side in the cochlear-shaped casing. Preferably, the rear casing in the motor is constituted so as to abut on the front casing via a good heat transfer member for complementing heat dissipation. The front casing in the motor includes a protruded heat dissipation enlarging surface on a ventilation passage side of the cochlear-shaped casing. A cylinder part outer peripheral edge of a bearing box formed integrally with the front casing of the motor is provided with a flange-shaped annular protrusion.