PURPOSE: To provide a cooling means for bearings, which support a rotary shaft of a turbine freely to turn, rationally.

CONSTITUTION: In an air motor A provided with a turbine 2, in which both ends of a rotary shaft 4 are supported by bearings 5, 6 freely to turn, the led compressed air is injected for supply into a turbine chamber 3 through an air supply flow passage 8, and thereafter, the exhaust air flowed from the turbine chamber 3 is exhausted through an exhaust flow passage 9. In this air motor A, the air supply flow passage 8 is made to contact to the bearing 5 for supporting one end of the rotary shaft 4 of the turbine 2, and the exhaust flow passage 9 is made to contact to the bearing 9 for supporting the other end of the rotary shaft 4.