In a housing 20 of an oil-cooled screw compressor 10, a separation gas supply path 59 through which separation gas is supplied to a separation gas supply gap 58 defined between a first seal unit and a second seal unit of a seal device 50, and a pressure balancing path 60 through which an area closer to a screw chamber 20a than the first seal unit in a discharge side seal chamber 20d communicates with a compression chamber at a pressure higher than an intake pressure and lower than a discharge pressure, are defined. A check valve 62 that restricts a flow of a fluid in a direction from the screw chamber 20a to the discharge side seal chamber 20d is disposed in the pressure balancing path 60.