A photoreactive compound represented by the following formula I: wherein in the formula I, Ra represents a cyano group, an amide group, a carboxyl group, a C2 to C7 alkoxycarbonyl group, a phosphono group, a sulfo group or a hydrogen atom, R1 and R2 each independently represent a cyano group, an amide group, a carboxyl group, a C2 to C7 alkoxycarbonyl group or a hydrogen atom, R3 is a hydrogen atom, a hydroxy group, a C1 to C3 alkoxy group, a C1 to C3 alkylsulfanyl group, a nitro group, a fluorine atom, a methyl fluoride group, a monovalent group of a C6 to C12 monocyclic or bicyclic aromatic compound, a monovalent group of a C6 to C12 monocyclic or bicyclic heterocyclic aromatic compound or a monovalent group represented by the following formula: wherein in the above formula, Ra, R1 and R2 represent groups selected from the groups listed for Ra, R1 and R2 described above with regard to the formula I independent of Ra, R1 and R2 described above with regard to the formula I, R4 represents a hydrogen atom or a Q 1 -O-CH 2 -group, R5 represents an -O-Q 1 group, a hydrogen atom, a methyl group or an ethyl group provided that R5 represents an -O-Q 1 group when R4 is a hydrogen atom, and R5 represents a hydrogen atom, a methyl group or an ethyl group when R4 is a Q 1 -O-CH 2 -group, R6 represents an -O-Q 2 group, a -CH 2 -O-Q 2 group or a -CH(CH 3)-O-Q 2 group, Q 1 represents a hydrogen atom, a phosphate group formed together with O attached to Q 1, a nucleotide or nucleic acid linked through a phosphodiester bond formed with a phosphate group formed together with O attached to Q 1 or a DMTr group, Q 2 represents a hydrogen atom, a phosphate group formed together with O attached to Q 2, a nucleotide or nucleic acid linked through a phosphodiester bond formed with a phosphate group formed together with O attached to Q 2, a group represented by the following formula: wherein the above formula represents a monovalent group having a free valency at P, or a group represented by the following formula: wherein the above formula represents a monovalent group having a free valency at P. Ra represents a cyano group, an amide group, a carboxyl group, a C2 to C7 alkoxycarbonyl group, a phosphono group, a sulfo group or a hydrogen atom, R1 and R2 each independently represent a cyano group, an amide group, a carboxyl group, a C2 to C7 alkoxycarbonyl group or a hydrogen atom, R3 is a hydrogen atom, a hydroxy group, a C1 to C3 alkoxy group, a C1 to C3 alkylsulfanyl group, a nitro group, a fluorine atom, a methyl fluoride group, a monovalent group of a C6 to C12 monocyclic or bicyclic aromatic compound, a monovalent group of a C6 to C12 monocyclic or bicyclic heterocyclic aromatic compound or a monovalent group represented by the following formula: wherein in the above formula, Ra, R1 and R2 represent groups selected from the groups listed for Ra, R1 and R2 described above with regard to the formula I independent of Ra, R1 and R2 described above with regard to the formula I, R4 represents a hydrogen atom or a Q 1 -O-CH 2 -group, R5 represents an -O-Q 1 group, a hydrogen atom, a methyl group or an ethyl group provided that R5 represents an -O-Q 1 group when R4 is a hydrogen atom, and R5 represents a hydrogen atom, a methyl group or an ethyl group when R4 is a Q 1 -O-CH 2 -group, R6 represents an -O-Q 2 group, a -CH 2 -O-Q 2 group or a -CH(CH 3)-O-Q 2 group, Q 1 represents a hydrogen atom, a phosphate group formed together with O attached to Q 1, a nucleotide or nucleic acid linked through a phosphodiester bond formed with a phosphate group formed together with O attached to Q 1 or a DMTr group, Q 2 represents a hydrogen atom, a phosphate group formed together with O attached to Q 2, a nucleotide or nucleic acid linked through a phosphodiester bond formed with a phosphate group formed together with O attached to Q 2, a group represented by the following formula: wherein the above formula represents a monovalent group having a free valency at P, or a group represented by the following formula: wherein the above formula represents a monovalent group having a free valency at P.