A curable silicone composition comprising: an organopolysiloxane having at least two alkenyl groups in a molecule; wherein further is an organopolysiloxane comprising 30 to 100 mass% of (A 1) an organopolysiloxane comprising a siloxane block represented by the general formula: -(R 1 R 2 SiO) m - (wherein, R 1 is an alkyl group having 1 to 6 carbon atoms or a phenyl group, R 2 is an alkenyl group having 2 to 10 carbon atoms, and m is a positive number in a range of 3 to 50); and 0 to 70 mass% of (A 2) an organopolysiloxane which does not have the above-mentioned siloxane block and which contains at least two alkenyl groups in a molecule; an organopolysiloxane having at least two silicon-bonded hydrogen atoms in a molecule, included at a quantity whereby an amount of silicon-bonded hydrogen atoms in the component is from 0.5 to 10 moles per 1 mole of the alkenyl groups in the component and wherein component is an organopolysiloxane comprising a siloxane block represented by the general formula: -(R 3 HSiO) n - (wherein, R 3 is an alkyl group having 1 to 6 carbon atoms or a phenyl group, and n is a positive number in a range of 3 to 100); a catalytic quantity of a hydrosilylation reaction catalyst; a spherical silica fine powder having a major axis to minor axis ratio of 1.5 or less and an average particle diameter of 50 μm or less, included at a quantity of 200 parts by mass or more relative to a total of 100 parts by mass of the component and the component; and glass fibers having an average fiber length of 1,000 μm or less and an average fiber diameter of 30 μm or less, included at a quantity of 25 parts by mass or more relative to a total of 100 parts by mass of the component and the component; wherein the total content of the component and the component is 900 parts by mass or less relative to the total of 100 parts by mass of the component and the component. an organopolysiloxane having at least two alkenyl groups in a molecule; wherein further is an organopolysiloxane comprising 30 to 100 mass% of (A 1) an organopolysiloxane comprising a siloxane block represented by the general formula: -(R 1 R 2 SiO) m - (wherein, R 1 is an alkyl group having 1 to 6 carbon atoms or a phenyl group, R 2 is an alkenyl group having 2 to 10 carbon atoms, and m is a positive number in a range of 3 to 50); and 0 to 70 mass% of (A 2) an organopolysiloxane which does not have the above-mentioned siloxane block and which contains at least two alkenyl groups in a molecule; an organopolysiloxane having at least two silicon-bonded hydrogen atoms in a molecule, included at a quantity whereby an amount of silicon-bonded hydrogen atoms in the component is from 0.5 to 10 moles per 1 mole of the alkenyl groups in the component and wherein component is an organopolysiloxane comprising a siloxane block represented by the general formula: -(R 3 HSiO) n - (wherein, R 3 is an alkyl group having 1 to 6 carbon atoms or a phenyl group, and n is a positive number in a range of 3 to 100); a catalytic quantity of a hydrosilylation reaction catalyst; a spherical silica fine powder having a major axis to minor axis ratio of 1.5 or less and an average particle diameter of 50 μm or less, included at a quantity of 200 parts by mass or more relative to a total of 100 parts by mass of the component and the component; and glass fibers having an average fiber length of 1,000 μm or less and an average fiber diameter of 30 μm or less, included at a quantity of 25 parts by mass or more relative to a total of 100 parts by mass of the component and the component;