Disclosed are a tension-maintaining unit of a continuous track device for a ship, and a continuous track device for a ship, having same. The tension-maintaining unit of a continuous track device for a ship of the present invention comprises: a first output part which is connected to a first rotating member of a continuous track main body and is provided with a first one-way bearing; a second output part which is connected to a second rotating member of the continuous track main body and is provided with a second one-way bearing; and a drive part which transfers power to the first output part and the second output part, wherein, while the second one-way bearing is driven by the power, the first one-way bearing freely rotates when the continuous track main body moves in the forward direction, and thus prevents the loosening of the tension of a first power transfer member provided on the continuous track main body, and, while the first one-way bearing is driven by the power, the second one-way bearing freely rotates when the continuous track main body moves in the backward direction, and thus prevents the loosening of the tension of the first power transfer member.