To provide an HIP apparatus capable of improving productivity without involving a problem to be caused by sealing performance, and also without making the diameter of a pressure container larger wastefully.

A hot isotropic pressing apparatus (HIP apparatus) 1 is provided with an axial-flow fan 15, whose number of rotations and rotational direction are variable, on the underside of a furnace chamber 8 surrounded by a gas circulating flow passage 14 within a pressure container 2. A controlling means 18 is provided which varies the axial-flow fan 15 to an operational condition where a natural convection current flowing downward through a vent hole 11 provided at an upper part of a heat-insulating layer 7 is balanced with a countercurrent flowing upward, through vent holes 12 provided at a lower part of the heat-insulating layer 7 in a holding time zone during the HIP processing, and to an operational condition where a forced convection current is caused by rotating the axial-flow fan 15 in a direction reverse to the rotational direction in the holding time zone during the HIP precessing in a subsequent cooling time zone.