To provide a method for selectively detecting the methylation of particular cytosines in genomic DNA using a methylcytosine detection method using an anti-methylcytosine antibody to improve quantitativity and reliability. A method for detecting the methylated state of cytosine at a specific position contained in a nucleic acid, includes fragmenting the nucleic acid using a restriction enzyme; forming a double-stranded nucleic acid between the fragmented nucleic acid and a single-stranded nucleic acid having a base sequence capable of hybridizing with the fragmented nucleic acid but incapable of resulting in the formation of a base pair with cytosine at a specific position in the fragmented nucleic acid and a solid phase-binding site; binding the double-stranded nucleic acid on a solid phase using the solid phase-binding site; and measuring the amount of an antibody binding to the double-stranded nucleic acid on the solid phase.