A hydrophilic substrate, comprising: a substrate having a surface containing at least one group represented by -N(R 1) 2 or -N(R 2) 3 + wherein each R 1 or R 2 is the same or different and represents a hydrogen atom or a substituted or unsubstituted hydrocarbon group optionally containing a hetero atom; and a hydrophilic polymer layer provided on the surface of the substrate, wherein the at least one group represented by -N(R 1) 2 or -N(R 2) 3 + is introduced by treating the surface of the substrate with a silane coupling agent containing the at least one group represented by -N(R 1) 2 or -N(R 2) 3 +, wherein the silane coupling agent is at least one selected from compounds of the formula, and: wherein R 11 and R 12 are the same or different and each represent a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 16 to R 18 are the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; and R 19 represents a substituted or unsubstituted divalent hydrocarbon group optionally containing a hetero atom, wherein R 11 to R 13 are the same or different and each represent a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 16 to R 18 are the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 19 represents a substituted or unsubstituted divalent hydrocarbon group optionally containing a hetero atom; and X represents a halogen, wherein R 21 to R 23 are the same or different and each represent a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 24 to R 26 are the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 27 to R 30 each represent a substituted or unsubstituted divalent hydrocarbon group optionally containing a hetero atom; X represents a halogen; and n represents the number of repetitions. a substrate having a surface containing at least one group represented by -N(R 1) 2 or -N(R 2) 3 + wherein each R 1 or R 2 is the same or different and represents a hydrogen atom or a substituted or unsubstituted hydrocarbon group optionally containing a hetero atom; and a hydrophilic polymer layer provided on the surface of the substrate, wherein the at least one group represented by -N(R 1) 2 or -N(R 2) 3 + is introduced by treating the surface of the substrate with a silane coupling agent containing the at least one group represented by -N(R 1) 2 or -N(R 2) 3 +, wherein the silane coupling agent is at least one selected from compounds of the formula, and: wherein R 11 and R 12 are the same or different and each represent a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 16 to R 18 are the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; and R 19 represents a substituted or unsubstituted divalent hydrocarbon group optionally containing a hetero atom, wherein R 11 to R 13 are the same or different and each represent a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 16 to R 18 are the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 19 represents a substituted or unsubstituted divalent hydrocarbon group optionally containing a hetero atom; and X represents a halogen, wherein R 21 to R 23 are the same or different and each represent a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 24 to R 26 are the same or different and each represent a substituted or unsubstituted monovalent hydrocarbon group optionally containing a hetero atom; R 27 to R 30 each represent a substituted or unsubstituted divalent hydrocarbon group optionally containing a hetero atom; X represents a halogen; and n represents the number of repetitions.