A hot isostatic pressing apparatus (HIP apparatus) comprises a vertically cylindrical high-pressure vessel comprising a high-pressure cylinder 1 and upper and lower lids 2 and 3; a bottomed cylindrical casing 6 capable of housing workpieces 9 and a resistance-wire heater 11, a heat insulating structure 16 equipped with a gas flow regulating valve 15 and formed in a bottomed cylindrical shape on the outside of the casing 6 so as to cover the casing 6, and a heat sink 17 having a water cooling mechanism provided in the space defined by the heat insulating structure 16 and the inner surface of the high-pressure cylinder 1, which are provided within the high-pressure vessel; and a pressure medium gas stirring fan 12 for promoting the temperature uniformity of the space of the treatment chamber 7 for housing the workpieces 9, the stirring fan being arranged on the lower lid 3 side within the casing 6, whereby the cooling to a temperature range of 100 C. or lower which allows a quenching treatment and the safe manual handling of workpieces can be efficiently performed.