To provide an antifouling tool used by being inserted through a rope laid or spanned in water for culturing laver, installing a fixed net or mooring a boat, etc., naturally scraping the rope always for peeling off aquatic organisms at an extremely initial stage of their attachment to prevent their gregarious growth.

This antifouling tool against the aquatic organisms 1 consisting of a tidal current-receiving plate part 3 for receiving the tidal current and a rope-inserted part 2 through which the rope is inserted as freely slidable so as to scrape the surface of the rope is characterized by having a floating up and down speed V in sea water prescribed in the specification, in a range: (-)500≤V≤500 cm/min, except for the laver-culturing net, and in the case of the laver-culturing net, it is in the range: 0<V≤500 cm/min.