To obtain a slime inhibitor on a water-flowing route.

This volatile slime inhibitor features being molded as a solid which contains a copper compound and a plant extract essential oil exhibiting microbicidal or antimicrobial effect by volatilizing in proportions of 0.1-10 wt.% and 1-48 wt.%, respectively, as essential components and shows a property gradually lost by flowing water together with an adhesive carrier capable of holding these components to exhibit a release control property. Antimicrobial activity, slime inhibition or malodor generation inhibitory effect is exerted by putting this solid into the water-flowing route.