[Problem]To provide an excellent oil thickening agent or gelling agent which has excellent compatibility with a variety of oil agent systems and which can freely control the form, viscosity and the like of an oil-based raw material or cosmetic composition by adjusting the added amount of the thickening agent or gelling agent. In addition, to provide a gel composition which is a base used to stably and easily produce cosmetic compositions having a variety of viscoelasticities and forms and which maintains a variety of oil agents in a gel form having an intermediate viscoelasticity between a liquid and a solid, and a cosmetic composition and the like comprising the thickening agent or gelling agent.[Means To Resolve the Problems]A thickening agent or gelling agent for an oil-based raw material, wherein the thickening agent or gelling agent has a hydrophilic group and a group having a siloxane dendron structure and which contains a novel co-modified organopolysiloxane preferably having a degree of polymerization of not lower than 200, and a topical composition or cosmetic composition containing the thickening agent or gelling agent. Furthermore, a gel composition containing the co-modified organopolysiloxane and a method for producing a cosmetic composition and the like by using the gel composition.
