To provide, so as to effectively utilize rosins, which are natural resources, from the standpoint of honoring environmental concern, a novel and useful rosinous reaction product and to use the reaction product for desired purposes.

The provided reaction product is obtained by epoxy-decyclizing and addition-reacting an active hydrogen-containing hydrazine and/or active hydrogen-containing imidazole and rosin glycidyl ester; the use of a reaction product obtained by epoxy-decyclizing an active hydrogen-containing hydrazine and/or active hydrogen-containing imidazole and active hydrogen-containing amine compound and rosin glycidyl ester is also proposed.