The present invention provides an organopolysiloxane obtained by binding, to at least two silicon atoms of an organopolysiloxane segment constituting a main chain, a poly(N-acylalkyleneimine) segment composed of a repeating unit represented by the following formula (1): wherein R1 represents a hydrogen atom or an alkyl group having from 1 to 3 carbon atoms and n is 2 or 3, via an alkylene group containing a hetero atom, wherein the poly(N-acylalkyleneimine) segment has a number-average molecular weight of from 1,600 to 3,500; a mass ratio (a/b) of the organopolysiloxane segment (a) constituting the main chain to the poly(N-acylalkyleneimine) segment (b) (which will hereinafter be called “mass ratio (a/b)”, simply) is from 42/58 to 58/42; the organopolysiloxane segment between two poly(N-acylalkyleneimine) segments adjacent to each other has a weight-average molecular weight of from 1,600 to 3,500; and the organopolysiloxane segment constituting the main chain has a weight-average molecular weight of 7,000 to 100,000.