Abstract: In a long hot water mat, straight parts (4a) of a hot water pipe (4) are laid lengthwise in a long mat body (2) and U-shaped turning parts (4b) of the hot water pipe are placed at locations near the opposite ends (2b) of the mat body (2). Slits (7) are formed at regular intervals in the lower surface of the mat body (2) so that the slits cross the mat body (2) in directions crossing the straight parts (4a) of the hot water pipe (4). The hot water mat having a heat dissipating sheet (6) thereon can be rolled from an end of the mat body (2), with the heat dissipating sheet being placed inward, due to the slits (7) so that the mat can be easily moved using an elevator or can be easily moved into a room while avoiding a reduction in the size of the mat.