A fire-extinguishing device for an open-type oil burner is disclosed which is capable of effectively preventing the discharge of bad odor to a room due to unburned fuel oil gas at the fire-extinguishing of the oil burner. The fire-extinguishing device includes a damper for closing, at the fire-extinguishing, an opening of a combustion cylinder construction of the oil burner through which combustion gas is discharge to a room. The damper or combustion cylinder construction may be provided with an oxidation catalyst plate through which combustion gas is discharged to a room at the fire-extinguishing, so that unburned fuel oil gas may be removed by means of the catalyst plate.