PURPOSE: To obtain the captioned highly heat-insulating and well-workable panel at a low cost by a method wherein expandable inorganic material mixed adhesive is coated on a hard base in the zigzag form, flaky high-radioactive foils are scattered on the base, expandable synthetic resin material is discharged on the foils.

CONSTITUTION: Expandable inorganic material mixed adhesive 6 is coated on incombustible hard base 2 in the dotted or zig-zag form, flaky high-radio-active foils 7 are scattered and expandable synthetic resin material 8 is discharged by a discharging machine 9. The base 2 is guided by a carrier 11 horizontally in a fixed direction and a continuous body is molded by the upper and lower molds 13, 14 of a mold 12 having a heating device 15. For that time a sheet matter 10 is laminated on material 8 and the laminated material is cut by a cutter 16 at a desired length to obtain a panel.