Abstract: A temperature control system for liquid plant is comprised of liquid metal, plant members, heaters for heating these liquid metal and the plant members at respective control points, a temperature control unit and a control unit. The plant members include a vessel containing liquid metal, pipe lines through which the liquid metal circulates, and valves. Further, temperature sensors, a level detector for detecting the level of the liquid metal, and a meter for detecting the flow rate of the liquid metal, are mounted to the plant members. Temperature sensors produce output signals relating to the condition parameter of the plant which data is delivered via an interface to the temperature control system and the control unit, as the information at each control point. The control unit previously stores the operating schedule of the plant members and transfers, the input signal relating to the plant condition to the temperature control system, with reference to the temperature control schedule.