To enhance a gas-liquid contact efficiency to thereby efficiently remove hydrogen sulfide without detriment to the quality of a sulfurized grease.

A reaction product comprising a sulfurized grease A, fed into an agitating tank 1, is sucked and withdrawn by a feed pump 3 from the inside wall part of the tank, and it is then fed into the mixer inlet 7 of a gas-liquid mixer 4. Air or a gas supplied from a highly concentrated oxygen supply unit 5 is fed into an ejector 10 serving as a gas supply port of the gas-liquid mixer 4, wherein the air or gas is mixed with the liquid reaction product. The mixture is discharged from a mixer outlet 8 and sent through a pipeline back to the agitating tank 1 for recycling.