PURPOSE: To obtain the subject vegetable having an ultrahigh nutritive value in a high yield in a cold northern district by sensing and regulating the room temperature in a greenhouse and quality of a fertilizer solution with sensors and sprinkling quartzite in cultivation bed soil in the greenhouse in the water culture utilizing a hot spring.

CONSTITUTION: In the water culture utilizing a hot spring, the room temperature in a greenhouse and the water quality of a fertilizer solution are regulated. Quartzite is sprinkled in cultivation bed soil of a cultivation vessel 10 in the greenhouse. The room temperature is regulated by keeping the water temperature constant with a boiler 1, supplying hot water to heat exchangers 2 on both sides of the greenhouse and feeding air warmed to the set temperature with the heat exchangers 2 to the whole greenhouse with a vinyl pipe 4. The quality of the fertilizer solution is regulated by feeding a fertilizer from a fertilizer (culture solution) tank 9 to the cultivation vessel 10 with a water feed pump 12 using a circulation system in the greenhouse, including air in the fertilizer with a liquid feed nozzle 14, flowing the fertilizer solution through the cultivation vessel 10, returning the fertilizer solution from a drain port to the fertilizer tank, recirculating the fertilizer solution through the cultivation vessel and automatically adding the fertilizer solution from agent tanks 7 with a controller 11 when the amount of the fertilizer solution is below the set value sensed with an EC sensor 8. Thereby, etch vegetable Corcharus oltorius L. 6 is cultivated by utilizing a hot spring.