A hot isostatic pressing device which includes a processing chamber to perform isostatic pressing processing to a workpiece by using pressure medium gas in the processing chamber, the hot isostatic pressing device comprising: a gas impermeable casing (3, 4) arranged to surround the workpiece; a heating unit provided inside the casing (3, 4) to form the processing chamber around the workpiece; a high-pressure container housing the heating unit and the casing (3, 4); a heat accumulator provided below the processing chamber, the heat accumulator being thermally exchanged with the pressure medium gas to promote cooling of the pressure medium gas; and a cooling promotion flow path formed in the casing (3, 4), wherein the casing (3, 4) is arranged to form a first circulation flow in which the pressure medium gas passes upward through an inner flow path in the casing (3, 4), passes downward through an outer flow path between an inner circumferential surface of the high-pressure container and an outer circumferential surface of the casing (3, 4), and then returns to the inner flow path, and to form a second circulation flow in which the pressure medium gas that has diverged from the first circulation flow is thermally exchanged with the workpiece inside the processing chamber in the casing (3, 4) and then returns to the first circulation flow, characterized in that, before the pressure medium gas of the second circulation flow thermally exchanged with the workpiece joins the pressure medium gas of the first circulation flow, the cooling promotion flow path guides the pressure medium gas of the second circulation flow to the heat accumulator to allow the pressure medium gas of the second circulation flow to be cooled by the heat accumulator, wherein the casing (3, 4) is configured to allow the pressure medium gas forming the first circulation flow and the pressure medium gas forming the second circulation flow to unite at a lower end of the inner flow path, the lower end being located below the processing chamber, wherein the heat accumulator is provided in a vertical position between the processing chamber and the lower end of the inner flow path, and wherein the pressure medium gas that has diverged from the second circulation flow is guided by the cooling promotion flow path to pass downward relative to the heat accumulator. a gas impermeable casing (3, 4) arranged to surround the workpiece; a heating unit provided inside the casing (3, 4) to form the processing chamber around the workpiece; a high-pressure container housing the heating unit and the casing (3, 4); a heat accumulator provided below the processing chamber, the heat accumulator being thermally exchanged with the pressure medium gas to promote cooling of the pressure medium gas; and a cooling promotion flow path formed in the casing (3, 4), wherein the casing (3, 4) is arranged to form a first circulation flow in which the pressure medium gas passes upward through an inner flow path in the casing (3, 4), passes downward through an outer flow path between an inner circumferential surface of the high-pressure container and an outer circumferential surface of the casing (3, 4), and then returns to the inner flow path, and to form a second circulation flow in which the pressure medium gas that has diverged from the first circulation flow is thermally exchanged with the workpiece inside the processing chamber in the casing (3, 4) and then returns to the first circulation flow, characterized in that, before the pressure medium gas of the second circulation flow thermally exchanged with the workpiece joins the pressure medium gas of the first circulation flow, the cooling promotion flow path guides the pressure medium gas of the second circulation flow to the heat accumulator to allow the pressure medium gas of the second circulation flow to be cooled by the heat accumulator, wherein the casing (3, 4) is configured to allow the pressure medium gas forming the first circulation flow and the pressure medium gas forming the second circulation flow to unite at a lower end of the inner flow path, the lower end being located below the processing chamber, wherein the heat accumulator is provided in a vertical position between the processing chamber and the lower end of the inner flow path, and wherein the pressure medium gas that has diverged from the second circulation flow is guided by the cooling promotion flow path to pass downward relative to the heat accumulator.