Abstract: An alga growing apparatus that includes a gas dissolving portion, an alga tank, first and second LEDs, a supplying portion, and a circulation pump portion. Gas dissolving portion dissolves carbon dioxide and oxygen into deep-ocean water to form growing water. The circulation pump portion sucks out and delivers the growing water and the nori thalli from the alga tank 30 to the gas dissolving portion and injects the growing water and the nori thalli into the alga tank upon passage through the gas dissolving portion and a supply pipe of the supplying portion. The supplying portion discharges the growing water and the nori thalli along a direction obliquely intersecting a curving direction of an inner side surface of the alga tank and the growing water flows inside the alga tank as an eddy flow.