Disclosed are a frictional resistance reducing device that effectively reduces the frictional resistance of a ship, and a ship including same. The frictional resistance reducing device comprises: a first air discharge part formed on the leading undersurface of a ship and discharging air into water; a second air discharge part formed behind the first air discharge part and discharging air into water; and an air supplying source supplying air to the first air discharge part and the second air discharge part, wherein the first air discharge part and the second air discharge part are disposed in-line along the lengthwise direction of the ship, and at least a portion of a first air discharge duration of the first air discharge part and at least a portion of a second air discharge duration of the second air discharge part overlap each other.