To provide a fertilizer tool for algae cultivation capable of efficiently supplying a fertilizer liquid without damaging algae.SOLUTION: There is provided a fertilizer tool 100 for algae cultivation for applying fertilizer to algae WM which are cultivated on a rope 1 provided in the water, the fertilizer tool comprising: a fertilization agent for algae cultivation including a liquid fertilizer being ionized； an extension container which is hollow and stores therein, the fertilization agent for algae cultivation and which is formed into a shape extended to one direction； and a fixture for fixing the extension container at a posture in which the extension direction thereof is along an extension direction of the rope 1. The extension container has on a part thereof, a semi-permeable membrane for transmitting ions of the fertilization agent for algae cultivation and not transmitting moisture, and is configured to elute ions of the fertilization agent for algae cultivation in the extension container through the semi-permeable membrane.SELECTED DRAWING: Figure 2
