An interlocking device for a HIP equipment that prevents possible damage to the HIP equipment arising from use of a furnace or processing gas in error and can control the oxygen concentration and pressure within the HIP equipment. The device includes a sensor for detecting a concentration of oxygen in the processing gas in a processing gas pipe system. If the sensor detects an excessively high oxygen concentration, a supply side interlocking mechanism closes a valve for the pipe system and disconnects a power source for a furnace in a high pressure vessel. A flow switch is connected to a safety pipe system having a safety device, and a thermocouple is provided for each of the safety and processing gas pipe systems and a relief pipe system. When the flow switch detects processing gas being spouted from the safety pipe system and/or when one of the temperature signals from the thermocouples exceeds a preset value, a relief side interlocking mechanism closes the processing gas pipe system, opens the relief pipe system, stops a gas compressor and disconnects the power source.