PURPOSE: To keep the fastening load between bearings constant regardless of the temperature difference between shafts and spacers by forming the spacers with a shape memory alloy in a bearing device provided with the spacers in a oil feed space between bearings arranged in parallel in the axial direction.

CONSTITUTION: An oil-free screw compressor has male and female rotors 6 and 7 stored in a casing 1, the rotors 6 and 7 are fitted to rotor shafts 8 and 9 respectively. Cylinder roller bearings 16-19, angular ball bearings 20 and 21, bearing outer wheel fixing plates 22-25, shaft seal devices 26-29, bearing oil feed nozzle inner wheel spacers 30 and 31 to secure an oil feed space, and oil feed nozzles 32 and 33 are provided as a bearing device rotatably supporting the shafts 8 and 9. In this case, the spacers 30 and 31 are formed with a shape memory alloy, the spacers 30 and 31 are set to maintain the integral shape and size at the operating temperature of a machine.