A guanidine derivative represented by formula (1), (2), (3) or its acid addition salt and a production process thereof ##STR1## wherein each of A and B is a C.sub.2 -C.sub.8 alkylene, D is a single bond, --CO-- or a C.sub.1 -C.sub.5 alkylene, E is H, a lower alkyl or the like, m is 1 to 6, n is 0 to 6 and R.sup.1 is H, a lower alkyl or the like, l is 1 to 10 and G is H, --OH or the like and a skin cosmetic containing the same. It can exert excellent keratin layer softening effect continuously for a long period of time.