A device for pretreatment of a sample for a protein sequencer comprising a high-performance liquid chromatograph, the device comprising: a vessel; a sample supply part configured to subject a protein sample to Edman degradation, and to introduce an amino acid obtained by Edman degradation in the sample supply part as a sample into the vessel; a reagent introduction part which is configured to introduce a reagent containing an organic solvent into the vessel so that the sample is dissolved in the reagent; a reagent discharge part which is configured to discharge the reagent in which a sample is dissolved in the vessel to an outside of the vessel; a first gas supply part which is configured to supply a gas into the vessel and thus pressurize an interior of the vessel; a second gas supply part which is different from the first gas supply part and which is configured to supply a gas into the reagent in the vessel and thus forms a gas bubble in the reagent; and a control unit; wherein the control unit performs; a first gas supply step of controlling gas supply from the first gas supply part, supplying a gas into the vessel and thus pressurizing an interior of the vessel; and a second gas supply step of controlling gas supply from the second gas supply part, supplying a gas into the reagent in the vessel and thus forming a gas bubble in the reagent so that the gas bubble volatilizes the organic solvent in the reagent; wherein the reagent discharge part is configured to discharge the reagent in the vessel from a reagent discharge tube to the high-performance liquid chromatograph after the first gas supply step and the second gas supply step; wherein the first gas supply part is configured to supply a gas into the vessel via the reagent introduction part, and the second gas supply part is configured to supply a gas into the reagent in the vessel via the reagent discharge part. a vessel; a sample supply part configured to subject a protein sample to Edman degradation, and to introduce an amino acid obtained by Edman degradation in the sample supply part as a sample into the vessel; a reagent introduction part which is configured to introduce a reagent containing an organic solvent into the vessel so that the sample is dissolved in the reagent; a reagent discharge part which is configured to discharge the reagent in which a sample is dissolved in the vessel to an outside of the vessel; a first gas supply part which is configured to supply a gas into the vessel and thus pressurize an interior of the vessel; a second gas supply part which is different from the first gas supply part and which is configured to supply a gas into the reagent in the vessel and thus forms a gas bubble in the reagent; and a control unit; wherein the control unit performs; a first gas supply step of controlling gas supply from the first gas supply part, supplying a gas into the vessel and thus pressurizing an interior of the vessel; and a second gas supply step of controlling gas supply from the second gas supply part, supplying a gas into the reagent in the vessel and thus forming a gas bubble in the reagent so that the gas bubble volatilizes the organic solvent in the reagent; a first gas supply step of controlling gas supply from the first gas supply part, supplying a gas into the vessel and thus pressurizing an interior of the vessel; and a second gas supply step of controlling gas supply from the second gas supply part, supplying a gas into the reagent in the vessel and thus forming a gas bubble in the reagent so that the gas bubble volatilizes the organic solvent in the reagent; wherein the reagent discharge part is configured to discharge the reagent in the vessel from a reagent discharge tube to the high-performance liquid chromatograph after the first gas supply step and the second gas supply step; wherein the first gas supply part is configured to supply a gas into the vessel via the reagent introduction part, and the second gas supply part is configured to supply a gas into the reagent in the vessel via the reagent discharge part.