To reduce access of heat from a heating value variation unit to a place where it is desired that thermal change is reduced.
On the basis of a difference between temperatures of a second fluid measured by a first thermometer 16 and by a second thermometer 17 as well as a flow rate of the second fluid measured by a flowmeter 18, a heating value controller 19 calculates a heating value of the second fluid. When the heating value of the second fluid exceeds a predetermined value, the heating value controller 19 controls control valves 14a and 14b, which control a flow rate of a first fluid between a first constant-temperature water circulating device 13 and radial flow passages 10a and 10b, and adjusts an increment of the flow rate of the first fluid. The heating value controller also controls the first constant-temperature water circulating device 13 and adjusts a decrease in temperature of the first fluid. As a result, the heating value of the second fluid becomes equal to or less than the predetermined value.