To enhance cooling effect, while preventing the corrosion of a frit part by the liquid medium and enlarging a liquid medium chamber.

A second panel 10 made of glass is arranged in front of a front surface panel 4 with a space between the front surface panel 4 to form a liquid medium chamber 12, and the liquid medium chamber 12 is filled with the liquid medium 14 for cooling. An outer surface of a frit part 8 is coated with a film 18 of the material, which does not react with the liquid medium 14 or has low reactivity with the medium, practically, a silicone resin film 18 over the whole thereof. The second panel 10 has an area larger than that of the front surface panel 14, and a sidewall 20 of the liquid medium chamber 11 for surrounding the second panel 10 is extended so as to surround the frit part 8 with a space between the outer surface of the frit part 8, and an edge 22 opposite to the second panel 10 is connected to a funnel 6 through an annular part 24.