PURPOSE: To precisely control culturing solution component by detecting electroconductivity of culturing solution, controlling the electroconductivity within fixed region and supplying insufficient amount of ionic component.

CONSTITUTION: Electroconductivity of culturing solution in a preparing tank 2 is detected by an electroconductivity sensor 6 and electroconductivity is adjusted within fixed region by controlling each ion-supplying pump 5 or diluting water-supplying valve 35. Next, each ionic component in the culturing solution is individually detected by each ion sensor 11 and ionic concentration of insufficient ionic component among essential ingredients is increased by controlling ion-supplying pump 5 to keep ionic concentration ratio in the culturing solution uniform.