TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Salt: The boric acid metal salt is barium borate, magnesium borate and/or calcium borate, preferably barium borate. Preferred Foam: The styrene resin foam is preferably obtained by further adding 0.2-10 weight parts of bentonite, hectorite and/or inorganic porous material, 0.1-5 weight parts of cyanuric acid, isocyanuric acid and/or their derivatives, and 0.2-6 weight parts of silica-type compound surface-treated titanium oxide, with respect to 100 weight parts of styrene resin.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The tertiary component (c) of foaming agent is water, carbon dioxide, nitrogen, methyl alcohol and/or ethyl alcohol, preferably water.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Salt: The boric acid metal salt is barium borate, magnesium borate and/or calcium borate, preferably barium borate. Preferred Foam: The styrene resin foam is preferably obtained by further adding 0.2-10 weight parts of bentonite, hectorite and/or inorganic porous material, 0.1-5 weight parts of cyanuric acid, isocyanuric acid and/or their derivatives, and 0.2-6 weight parts of silica-type compound surface-treated titanium oxide, with respect to 100 weight parts of styrene resin.    TECHNOLOGY FOCUS - POLYMERS - Preferred Properties: The styrene resin foam has both thermal insulation property and flame retardance coinciding with three sorts of extrusion-method polystyrene foam heat insulating boards based on JIS A9511. The resin foam has heat conductivity of 0.028 W/mk or less. Combustibility of the resin foam is measured, and it is found that the flame disappears within 3 seconds. SPECIFIC COMPOUNDS - 3-5C saturated hydrocarbon is propane, n-butane and/or i-butane. Phosphorus base flame retarder is triphenyl phosphate and/or tris(tribromo neopentyl)phosphate. Halogenated flame retardant is hexabromo cyclo dodecane, tetrabromo cyclo octane and/or tetrabromo bisphenol A bis(allyl ether).    EXAMPLE - KPS (polystyrene resin having melt index of 3.1) (in weight parts) (100), talc (0.5), calcium stearate (0.3), hexabromo cyclo dodecane (4), CR900 (tris(tribromo neopentyl)phosphate) (1), BUSAN11 (barium borate) (1), synthetic hectorite (0.5) and silicon oxide (0.3) were mixed. The obtained resin mixture was supplied to an extruder, melted and extruded to obtain an extrusion-foamed component. Isobutane (4), methyl chloride (4) and water (0.8) were supplied with respect to polystyrene resin (100) from front-end vicinity of extruder, and resin foam was obtained. The obtained resin foam had thermal conductivity of 0.027 W/mk and density of 30 kg/m3. The area ratio of gas bubbles having diameter of 0.25 mm or less in the obtained foam was 35%.