The present invention relates to an organopolysiloxane graft polymer including an organopolysiloxane segment as a main chain thereof and an unsaturated monomer-derived copolymer segment containing a repeating unit derived from an unsaturated monomer containing a carboxylic acid or a carboxylic acid salt as a side chain thereof, in which a content of the organopolysiloxane segment in the organopolysiloxane graft polymer is 35 to 59% by mass, a content of the repeating unit derived from the unsaturated monomer containing a carboxylic acid or a carboxylic acid salt in the organopolysiloxane graft polymer is 4 to 17% by mass, and a content of a repeating unit derived from an unsaturated monomer whose homopolymer has a glass transition point of not lower than 150° C. (except for the unsaturated monomer containing a carboxylic acid or a carboxylic acid salt) in the organopolysiloxane graft polymer is not more than 14% by mass, and a number-average molecular weight of the organopolysiloxane segment is not less than 8,000 and not more than 200,000.