To provide a device and a method for supplying seawater enabled in efficient uplift by substantially reducing an energy loss, decreasing a temperature of cooling water and reducing the amount of water taken from, and saving energy in the uplift of the cooling water.

A seawater supply device 1 pumps up seawater (A) and supply it to equipment 10 as cooling water, and includes a bubble generating means 20 which is provided in the seawater (A) to generate bubbles B, a pump-up pipe 30 to pump up the bubbles B by the bubble generating means 20 and the seawater (A) to the sea, a tank 40 to store the bubbles B and the seawater (A) pumped up by the pump-up pipe 30, and a supply means 50 to supply the seawater (A) in the tank 40 to the equipment 10.