A pressure sensitive adhesive layer-forming organopolysiloxane composition, comprising: a chain organopolysiloxane having alkenyl groups in numbers greater than 1 on average within the molecule; an organopolysiloxane resin mixture comprising the following components and at a mass ratio of 1:99 to 99:1: an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups with respect to all silicon atoms in the molecule is 9 mole% or less, and the weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography is 4500 or more; and an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups with respect to all silicon atoms in the molecule is 9 mole% or less, and the weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography is less than 4500; an organohydrogenpolysiloxane having at least two Si-H bonds in the molecule; and an effective amount of a hydrosilylation reaction catalyst, wherein the mass ratio of component to component is within a range of 0.9 to 2.0, and the shear storage elastic modulus G' determined in accordance with the method outlined in the description at -20°C of a pressure sensitive adhesive layer obtained by curing the composition is within a range of 0.01 to 0.75 MPa. a chain organopolysiloxane having alkenyl groups in numbers greater than 1 on average within the molecule; an organopolysiloxane resin mixture comprising the following components and at a mass ratio of 1:99 to 99:1: an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups with respect to all silicon atoms in the molecule is 9 mole% or less, and the weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography is 4500 or more; and an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups with respect to all silicon atoms in the molecule is 9 mole% or less, and the weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography is less than 4500; an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups with respect to all silicon atoms in the molecule is 9 mole% or less, and the weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography is 4500 or more; and an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups with respect to all silicon atoms in the molecule is 9 mole% or less, and the weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography is less than 4500; an organohydrogenpolysiloxane having at least two Si-H bonds in the molecule; and an effective amount of a hydrosilylation reaction catalyst, wherein the mass ratio of component to component is within a range of 0.9 to 2.0, and the shear storage elastic modulus G' determined in accordance with the method outlined in the description at -20°C of a pressure sensitive adhesive layer obtained by curing the composition is within a range of 0.01 to 0.75 MPa.