PROBLEM TO BE SOLVED: To provide a water-insoluble support capable of easily immobilizing a ligand, to which a substance to be adsorbed such as endotoxin can be adsorbed, so as to allow the ligand to be able to exert its functions.SOLUTION: The water-insoluble support includes a base material and a linker that is bound to the base material, which is represented by formula 1 below, wherein Bn denotes a benzil group, x denotes a number ranging from 2 to 6, B denotes a protective group or a hydrogen atom, and * indicates the binding with the base material.