H.sub.2COOH, --SO.sub.2N(R)--, and each of s and t is an integer of 1 to 3, and salts thereof, e.g., trade name Sumimold FA [product of Sumico Lubricant Co., Ltd.].Of the aforementioned internal release agent (C), the preferred from the viewpoint of release properties include carboxy-modified organopolysiloxanes (c1) (in this paragraph, hereinafter (c1)) or ether-modified organopolysiloxanes (c3)