Abstract: To provide a fin attachment structure capable of attaching a fin detachably and easily on a board without using any tools, and particularly, to a fin attachment structure capable of reducing the damage to human body as much as possible when the fin comes into contact with the human body during surfing etc. and having an extremely high safety, and a fin. The above problem can be solved by a fin attachment structure and a fin, in which a groove part is provided on the bottom surface of the surfboard and a hollow part 10 is provided on the inner surface thereof, the hollow parts being further provided at the opposing positions on both side surfaces of the groove part, and an elastic member is provided at the deep side within the hollow part and a bail part at the opening side for biasing in the direction in which it projects to outside, wherein by the insertion of the fin attachment base portion into the groove part, the fin is biased and sandwiched and held by the ball part.