Device for winding/unwinding a flexible covering over a swimming pool, comprising: - Electrical motorised means suitable for rotating a shaft equipped with a primary coupling device, this primary coupling device being able to operate with a secondary coupling device of a complementary form, secured to a winding bar fitted to the flexible covering at at least one of its edges, - An independent electrical power source to supply power to the motorised means; - An electrically-operated element to supply power to the motorised means; characterised in that it comprises: - A casing having a circular shape, in which the motorised means and the independent electrical power source are fitted, the said casing comprising:. An outer rolling surface for rolling up on the ground along the pool;. Two parallel openings (22, 23) on either side of the outer rolling surface; - A motorised mobile assembly to position the said shaft in a proximal region of the casing and parallel to an axis of revolution of the said casing, with the said motorised mobile assembly comprising:. The said electrical motorised means;. The said independent electrical power source;. Two parallel plates (31, 32), each fitted at either openings (22, 23) of the casing;. Securing means forming a spacer and helping to maintain the two parallel plates (31, 32) at equal distances; - Guiding means for connecting the motorised mobile assembly by pivoting pins with regard to the casing. - Electrical motorised means suitable for rotating a shaft equipped with a primary coupling device, this primary coupling device being able to operate with a secondary coupling device of a complementary form, secured to a winding bar fitted to the flexible covering at at least one of its edges, - An independent electrical power source to supply power to the motorised means; - An electrically-operated element to supply power to the motorised means; - A casing having a circular shape, in which the motorised means and the independent electrical power source are fitted, the said casing comprising:. An outer rolling surface for rolling up on the ground along the pool;. Two parallel openings (22, 23) on either side of the outer rolling surface;. An outer rolling surface for rolling up on the ground along the pool;. Two parallel openings (22, 23) on either side of the outer rolling surface; - A motorised mobile assembly to position the said shaft in a proximal region of the casing and parallel to an axis of revolution of the said casing, with the said motorised mobile assembly comprising:. The said electrical motorised means;. The said independent electrical power source;. Two parallel plates (31, 32), each fitted at either openings (22, 23) of the casing;. Securing means forming a spacer and helping to maintain the two parallel plates (31, 32) at equal distances;. The said electrical motorised means;. The said independent electrical power source;. Two parallel plates (31, 32), each fitted at either openings (22, 23) of the casing;. Securing means forming a spacer and helping to maintain the two parallel plates (31, 32) at equal distances; - Guiding means for connecting the motorised mobile assembly by pivoting pins with regard to the casing.