A method for producing an inorganic substance powder highly-blended thin film sheet that blends and kneads inorganic substance powder, thermoplastic resin and an auxiliary agent at predetermined blending rates, molds and then draws to finish into a thin film sheet, the method comprising: a step of preparing the inorganic substance powder, the thermoplastic resin and the auxiliary agent, wherein the inorganic substance powder has an average particle size of 0.5 to 15 μm and is free of particles with a particle size of at least 50 μm; a step of molding an inorganic substance powder highly-blended thin film sheet intermediate body by setting a weight ratio of the inorganic substance powder to the thermoplastic resin to 60:40 to 82:18, blending the auxiliary agent at 0.05% by weight to 4.0% by weight based on the total amount of the inorganic substance powder and the thermoplastic resin being 100% by weight, and charging as starting materials into an extrusion molding machine equipped with twin screws, thereby causing high shearing stress to act on and knead the starting materials, extruding by way of a T die system by pushing the starting materials thus kneaded through a die, immediately followed by causing to contact a roll that is 50°C or higher and molding; and a step of performing longitudinal drawing and/or horizontal drawing so that the thin film sheet after drawing has a desired apparent specific gravity, by controlling drawing ratios in the longitudinal direction and horizontal direction both to 1.1 times to 3.0 times, wherein the thermoplastic resin is selected so as to be able to cause the apparent specific gravity of the inorganic substance powder highly-blended thin film sheet to decrease to 0.55 to 1.40 when establishing drawing ratios of 1.1 times to 3.0 times, wherein the desired apparent specific gravity is adjusted to the range of 0.55 to 1.40 to be white and opaque by selecting the thermoplastic resin in the above-mentioned way in the step of performing drawing, and wherein the thermoplastic resin is at least one type of resin selected from the group consisting of polyethylene, polypropylene and polystyrene. a step of preparing the inorganic substance powder, the thermoplastic resin and the auxiliary agent, wherein the inorganic substance powder has an average particle size of 0.5 to 15 μm and is free of particles with a particle size of at least 50 μm; a step of molding an inorganic substance powder highly-blended thin film sheet intermediate body by setting a weight ratio of the inorganic substance powder to the thermoplastic resin to 60:40 to 82:18, blending the auxiliary agent at 0.05% by weight to 4.0% by weight based on the total amount of the inorganic substance powder and the thermoplastic resin being 100% by weight, and charging as starting materials into an extrusion molding machine equipped with twin screws, thereby causing high shearing stress to act on and knead the starting materials, extruding by way of a T die system by pushing the starting materials thus kneaded through a die, immediately followed by causing to contact a roll that is 50°C or higher and molding; and a step of performing longitudinal drawing and/or horizontal drawing so that the thin film sheet after drawing has a desired apparent specific gravity, by controlling drawing ratios in the longitudinal direction and horizontal direction both to 1.1 times to 3.0 times, wherein the thermoplastic resin is selected so as to be able to cause the apparent specific gravity of the inorganic substance powder highly-blended thin film sheet to decrease to 0.55 to 1.40 when establishing drawing ratios of 1.1 times to 3.0 times, wherein the desired apparent specific gravity is adjusted to the range of 0.55 to 1.40 to be white and opaque by selecting the thermoplastic resin in the above-mentioned way in the step of performing drawing, and wherein the thermoplastic resin is at least one type of resin selected from the group consisting of polyethylene, polypropylene and polystyrene.