A dental air turbine (10) includes a turbine blade (12), a rotating shaft (11) which is integrally fixed with the turbine blade (12), and a pair of rolling bearings (13, 14) which rotatably support the rotating shaft (11) with respect to a housing (15). The pair of rolling bearings (13, 14) are arranged back-to-back while fitting inner rings (23, 24) on the rotating shaft (11) such that a preload is applied thereto. Accordingly, it is possible to reduce the sizes of the rolling bearings (13, 14) and to improve the moment rigidity of the rotating shaft (11).
