PURPOSE: To improve workability during a mounting work and firmly hold a fire-preventive glass panel upon occurrence of a fire by using a material capable of giving an expansion factor equal to or above the preset value for the prescribed temperature range, as a bulking agent for filling a gap between an interior wall and a fire-preventive glass panel.

CONSTITUTION: A setting block 3 is provided on the bottom of the mounting groove 2a of a window frame 2. Then, a fire-preventive glass panel 1 is inserted in the groove 2a, while the peripheral edge thereof being kept in contact with the block 3. Thereafter, gaps 7a and 7b formed between the glass panel 1 and the inner surface of the groove 2a are filled with a thermally expansible bulking agent 8. In this case, a material capable of giving an expansion factor approximately two times as large as the preset value over a temperature range from 100 to 950°C is used as the bulking agent 8. According to this construction, the glass panel 1 can be firmly held, and excellent fire-preventive function can be provided, when a fire takes place.