The present invention provides a technique by which heat can be efficiently recovered from a coolant used to cool a reactor, and contamination with dopant impurities from an inner wall of a reactor when polycrystalline silicon is deposited within the reactor can be reduced to produce high-purity polycrystalline silicon. With the use of hot water 15 having a temperature higher than a standard boiling point as a coolant fed to the reactor 10, the temperature of the reactor inner wall is kept at a temperature of not more than 370° C. Additionally, the pressure of the hot water 15 to be recovered is reduced by a pressure control section provided in a coolant tank 20 to generate steam. Thereby, a part of the hot water is taken out as steam to the outside, and reused as a heating source for another application.