A nucleic acid detection method for detecting an amplified double-stranded DNA fragment amplified by a nucleic acid amplification method, wherein: the amplified DNA fragment has a first substance binding site to which a first substance is specifically bindable, and a second substance binding site to which a second substance is specifically bindable, the first substance and the second substance being nucleic acid binding protein, namely a methylase; the amplified DNA fragment is a double-stranded DNA fragment obtained by the nucleic acid amplification method by use of two primers; one of the two primers has a base sequence to which the first substance is bindable in a double strand formed by binding the one of the two primers to a complementary strand, and the other of the two primers has a base sequence to which the second substance is bindable in a double strand formed by binding the other one of the two primers to a complementary strand; and the method comprising the steps of: (i) on a stationary-phase medium to which the first substance is immobilized, placing the amplified DNA fragment in a first region, and placing the second substance to which the labelling substance is bound in a third region, the first region and third region being different from each other and being different from a second region in which the first substance is immobilized; (ii) diffusing the amplified DNA fragment by use of a solvent to the third region; (iii)forming a complex in the third region by binding the amplified DNA fragment to the second substance to which the labelling substance is bound; (iv) further diffusing the complex by use of the solvent on the stationary-phase medium, to the second region; and (v) concentrating the amplified DNA fragment by causing the complex to bind to the first substance in the second region. the amplified DNA fragment has a first substance binding site to which a first substance is specifically bindable, and a second substance binding site to which a second substance is specifically bindable, the first substance and the second substance being nucleic acid binding protein, namely a methylase; the amplified DNA fragment is a double-stranded DNA fragment obtained by the nucleic acid amplification method by use of two primers; one of the two primers has a base sequence to which the first substance is bindable in a double strand formed by binding the one of the two primers to a complementary strand, and the other of the two primers has a base sequence to which the second substance is bindable in a double strand formed by binding the other one of the two primers to a complementary strand; and the method comprising the steps of: (i) on a stationary-phase medium to which the first substance is immobilized, placing the amplified DNA fragment in a first region, and placing the second substance to which the labelling substance is bound in a third region, the first region and third region being different from each other and being different from a second region in which the first substance is immobilized; (ii) diffusing the amplified DNA fragment by use of a solvent to the third region; (iii)forming a complex in the third region by binding the amplified DNA fragment to the second substance to which the labelling substance is bound; (iv) further diffusing the complex by use of the solvent on the stationary-phase medium, to the second region; and (v) concentrating the amplified DNA fragment by causing the complex to bind to the first substance in the second region. (i) on a stationary-phase medium to which the first substance is immobilized, placing the amplified DNA fragment in a first region, and placing the second substance to which the labelling substance is bound in a third region, the first region and third region being different from each other and being different from a second region in which the first substance is immobilized; (ii) diffusing the amplified DNA fragment by use of a solvent to the third region; (iii)forming a complex in the third region by binding the amplified DNA fragment to the second substance to which the labelling substance is bound; (iv) further diffusing the complex by use of the solvent on the stationary-phase medium, to the second region; and (v) concentrating the amplified DNA fragment by causing the complex to bind to the first substance in the second region.