PROBLEM TO BE SOLVED: To save energy required for heating and sterilizing a nutrient solution in hydroponics. SOLUTION: In this system for circulating a nutrient solution, a nutrient solution S after being heated and sterilized is flown in an internal pipe 8 of a double pipes 6 comprising an external pipe 7 and the internal pipe 8, a nutrient solution S before heating is flown in the external pipe 7, the nutrient solution after being heated and sterilized is cooled by heat exchange between the two nutrient solutions and fed to a hydroponics bed 1 and the nutrient solution S before heating is introduced to a heater 15 after heating by the heat exchange.
