To obtain an anti-fog agent which prevents an accident caused by an electric leak and which costs low in an electric-power expense by installing on the back of a mirror a hot-water supply tube which extends to the hot-water supply tap with reference to a mirror with a hot-water supply tube being fed in its vicinity.

A washstand 1 installed on the wall W of a bathroom is formed by a hollow vertical part 1a and a horizontal part 1b nearly in an L-shape. A mirror 2 is fixed at four corners by bolts 3 in the center of the vertical part 1a. A hot-water supply tube 7 is branched from the hot-water supply main tube penetrating the wall W with a part of the tube 7 being installed in parallel on the back of the mirror in a reversed U-letter shape. The head of the hot-water supply tube 7 is connected to a hot-water supply tap 8 installed on the front face of the horizontal part 1b. A part of the hot-water supply tube 7 is installed in a reversed U-letter shape and over the top of the hot-water supply tube a screw 10 as an air removal valve is installed. When the mirror 2 installed in the bathroom is blurred, releasing the hot-water supply tap 8 causes to supply hot water to a part of the hot-water supply tube 7 installed on the back of the mirror 2 and to raise the surface temperature of the mirror higher than that of the surrounding area. Accordingly, the blur on the mirror 2 is prevented.