A polyorganosiloxane composition for molding comprising: (A) a straight-chain polyorganosiloxane having two or more alkenyl groups bonded to silicon atoms, on average, in one molecule and having a viscosity at 25°C of 50,000 to 500,000 mPa·s; (B) 30 to 80 mass% of a polyorganosiloxane relative to a total of the (A) component and this component (B), the polyorganosiloxane including a resin structure containing a monofunctional siloxane unit represented by a formula: R 1 3 SiO 1/2 wherein R 1 s independently represent an alkenyl group or a substituted or unsubstituted alkyl group, a bifunctional siloxane unit represented by a formula: R 1 2 SiO 2/2 wherein R 1 s are as in the above, and a tetrafunctional siloxane unit represented by a formula: SiO 4/2 , at a molar ratio of a:b:c, on average where 0.3 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.1, 0.4 ≤ c ≤ 0.7, and a relation of a + b + c = 1 is satisfied, and having two or more alkenyl groups bonded to silicon atoms, on average, in one molecule; (C) an amount of a polyorganohydrogensiloxane having a hydrogen atom bonded to a silicon atom, an average degree of polymerization of 10 or more, a content of the hydrogen atom of 5.0 mmol/g or more and 11.0 mmol/g or less, and a weight decrease rate of 2.0 wt% or less when measured by thermogravimetric analysis (TGA) performed under the condition that the temperature is increased at a temperature increasing rate of 5 °C per minute from room temperature up to 140 °C, the amount of the polyorganohydrogensiloxane being set so that an amount of Si-bonded hydrogen in this component is 1.0 to 3.0 mol relative to a total 1 mol of the alkenyl group in the (A) component and the alkenyl group in the (B) component, wherein the (C) component is obtained by a method selected from a method of heating to 130°C or higher under a reduced pressure condition, a method of performing thin-film distillation, and a method of performing molecular distillation; and (D) a catalytic amount of a hydrosilylation reaction catalyst. (A) a straight-chain polyorganosiloxane having two or more alkenyl groups bonded to silicon atoms, on average, in one molecule and having a viscosity at 25°C of 50,000 to 500,000 mPa·s; (B) 30 to 80 mass% of a polyorganosiloxane relative to a total of the (A) component and this component (B), the polyorganosiloxane including a resin structure containing a monofunctional siloxane unit represented by a formula: R 1 3 SiO 1/2 wherein R 1 s independently represent an alkenyl group or a substituted or unsubstituted alkyl group, a bifunctional siloxane unit represented by a formula: R 1 2 SiO 2/2 wherein R 1 s are as in the above, and a tetrafunctional siloxane unit represented by a formula: SiO 4/2 , at a molar ratio of a:b:c, on average where 0.3 ≤ a ≤ 0.6, 0 ≤ b ≤ 0.1, 0.4 ≤ c ≤ 0.7, and a relation of a + b + c = 1 is satisfied, and having two or more alkenyl groups bonded to silicon atoms, on average, in one molecule; (C) an amount of a polyorganohydrogensiloxane having a hydrogen atom bonded to a silicon atom, an average degree of polymerization of 10 or more, a content of the hydrogen atom of 5.0 mmol/g or more and 11.0 mmol/g or less, and a weight decrease rate of 2.0 wt% or less when measured by thermogravimetric analysis (TGA) performed under the condition that the temperature is increased at a temperature increasing rate of 5 °C per minute from room temperature up to 140 °C, the amount of the polyorganohydrogensiloxane being set so that an amount of Si-bonded hydrogen in this component is 1.0 to 3.0 mol relative to a total 1 mol of the alkenyl group in the (A) component and the alkenyl group in the (B) component, wherein the (C) component is obtained by a method selected from a method of heating to 130°C or higher under a reduced pressure condition, a method of performing thin-film distillation, and a method of performing molecular distillation; and (D) a catalytic amount of a hydrosilylation reaction catalyst. <EOS>