To reduce the size of a hull and lower the manufacturing cost of a ship.

When the hull 2 is moved forward at a slow speed, a laver cultivating net 24 is guided by a guide member 9 to be passed from the bow end to the stern end and passed through an activating processing solution tray 21, an activating processing solution W force-fed from a supply path 22 of an activating processing solution tank 16 integrated with the hull 2 by a pump 23 is sprayed to the laver of the laver cultivating net 24 by a spray nozzle 26 in front of the activating processing solution tray 21, and the recovered surplus activating processing solution W is returned to the activating processing solution tank 16 by an exhaust passage 26 in rear of the activating processing solution tray 21 and circulated.