To provide an oil feeding method and an oil feeding mechanism for setting pressure in a seal chamber for housing a shaft seal device of an oil-cooled screw compressor to substantially constant pressure in unloaded operation and full load operation.

The oil-cooled screw compressor 1 is formed by arranging the seal chamber 70 on the suction side of a rotor chamber 13, and is provided with an oil feeding passage 30 opening in this seal chamber 70 and an oil feeding circuit 90 for introducing lubricating oil from a receiver tank into the oil feeding passage 30. This oil feeding circuit 90 is provided with a flow rate changing means for varying a lubricating oil quantity flowing in the circuit 90. This flow rate changing means increases a supply quantity of the lubricating oil in unloaded operation of the screw compressor 1 to a supply quantity of the lubricating oil in full load operation of the screw compressor 1.