A coating agent comprising: a hydroxyl-group-containing polyorganosiloxane represented by the following general formula: where R 1 and R 1' each independently represent a monovalent hydrocarbon group or a hydroxyl group (-OH), provided that at least one of R 1 and at least one of R 1' are hydroxyl groups (-OH), R 2 each independently represents a monovalent hydrocarbon group, and m is an integer of 1,000 to 30,000; a polydiorganosiloxane represented by the following general formula: where R 4 and R 5 each independently represent a monovalent hydrocarbon group, and n is an integer of 8 to 1,000; and an amino-group-containing polyorganosiloxane containing at least one amino group in one molecule thereof represented by the following general formula: where R 6 each independently represents a monovalent hydrocarbon group or a -OR 9 group, provided that R 9 each independently represents a substituted or unsubstituted C 1 -C 4 monovalent hydrocarbon group, R 7 and R 8 each independently represent a monovalent hydrocarbon group, A each independently represents an amino-group-containing group, p:q = (5 to 100):1, and q is an integer of 1 to 100, wherein the polydiorganosiloxane is contained in a proportion of a mass ratio to the amino-group-containing polyorganosiloxane of from 0.7 to 3.0, and the hydroxyl-group-containing polyorganosiloxane is contained in a proportion of 2.4 to 5.5 mass%, based on the total mass of the hydroxyl-group-containing polyorganosiloxane, the polydiorganosiloxane, and the amino-group-containing polyorganosiloxane. a hydroxyl-group-containing polyorganosiloxane represented by the following general formula: where R 1 and R 1' each independently represent a monovalent hydrocarbon group or a hydroxyl group (-OH), provided that at least one of R 1 and at least one of R 1' are hydroxyl groups (-OH), R 2 each independently represents a monovalent hydrocarbon group, and m is an integer of 1,000 to 30,000; where R 1 and R 1' each independently represent a monovalent hydrocarbon group or a hydroxyl group (-OH), provided that at least one of R 1 and at least one of R 1' are hydroxyl groups (-OH), R 2 each independently represents a monovalent hydrocarbon group, and m is an integer of 1,000 to 30,000; a polydiorganosiloxane represented by the following general formula: where R 4 and R 5 each independently represent a monovalent hydrocarbon group, and n is an integer of 8 to 1,000; and where R 4 and R 5 each independently represent a monovalent hydrocarbon group, and n is an integer of 8 to 1,000; and an amino-group-containing polyorganosiloxane containing at least one amino group in one molecule thereof represented by the following general formula: where R 6 each independently represents a monovalent hydrocarbon group or a -OR 9 group, provided that R 9 each independently represents a substituted or unsubstituted C 1 -C 4 monovalent hydrocarbon group, R 7 and R 8 each independently represent a monovalent hydrocarbon group, A each independently represents an amino-group-containing group, p:q = (5 to 100):1, and q is an integer of 1 to 100, wherein the polydiorganosiloxane is contained in a proportion of a mass ratio to the amino-group-containing polyorganosiloxane of from 0.7 to 3.0, and the hydroxyl-group-containing polyorganosiloxane is contained in a proportion of 2.4 to 5.5 mass%, based on the total mass of the hydroxyl-group-containing polyorganosiloxane, the polydiorganosiloxane, and the amino-group-containing polyorganosiloxane. where R 6 each independently represents a monovalent hydrocarbon group or a -OR 9 group, provided that R 9 each independently represents a substituted or unsubstituted C 1 -C 4 monovalent hydrocarbon group, R 7 and R 8 each independently represent a monovalent hydrocarbon group, A each independently represents an amino-group-containing group, p:q = (5 to 100):1, and q is an integer of 1 to 100,