PROBLEM TO BE SOLVED: To prevent diffusion of disease damage by effectively sterilizing disease damage fungus in a culture medium after inhibiting plant growth inhibition, in a cleaning method and cleaning facility which clean the culture medium by electrolyzing the culture medium.SOLUTION: An electrolysis is performed so that the total residual chlorine concentration in a culture medium becomes 1.0 mg-Cl/L or less. Even if the total residual chlorine concentration of the hypochlorous acid produced by electrolysis in the culture medium is a low concentration of 1.0 mg-Cl/L or less, a sufficient sterilization effect is obtained, and thereby sterilization treatment in such a low concentration can inhibit plant growth inhibition.
