A method for amplifying and detecting a target nucleotide sequence in a sample, the method comprising carrying out an amplification method and observing whether or not the amplification reaction product has been generated, wherein the amplification method is a method for amplification of nucleic acid at constant temperature using double-stranded nucleic acid as a template wherein one strand of the double-stranded nucleic acid comprises regions F3c, F2c, F1c, R1, R2 and R3 from the 3'-side of the double-stranded nucleic acid and wherein the other stand of the double-stranded nucleic acid comprises the complementary regions F3, F2, F1, R1 c, R2c and R3c from the 5' side of the double-stranded nucleic acid, wherein the method comprises: a) incubating a double-stranded nucleic acid template and an inner primer RA constituted by regions R1c and R2, whereby region R2 anneals to region R2c on the double-stranded nucleic acid template in the presence of a DNA polymerase that catalyzes a complementary strand synthesis reaction accompanying strand displacement, under a condition where the double-stranded nucleic acid is unstable using the inner primer RA as an origin, such that a region F2c of the target template nucleic acid to be annealed by an inner primer FA constituted by regions F1c and F2, whereby region F2 anneals to region F2c on the double-stranded nucleic acid template that is capable of amplifying the template nucleic acid at a constant temperature when the released single strand intramolecularly anneals with itself b) annealing a outer primer F3 to the region F3c of the single strand displaced in the step a), which is placed in a condition such that it can undergo base pairing; c) carrying out the complementary strand synthesis using the outer primer F3 as a synthesis origin, whereby the extended product synthesized using the inner primer FA as the origin is displaced and released as a single strand; and d) using the single strand as a template the inner primer RA and the outer primer R3, whereby region R2 anneals to region R2c, and R3 anneals to region R3c in the single strand displaced in step c) and initiate complementary strand synthesis. a) incubating a double-stranded nucleic acid template and an inner primer RA constituted by regions R1c and R2, whereby region R2 anneals to region R2c on the double-stranded nucleic acid template in the presence of a DNA polymerase that catalyzes a complementary strand synthesis reaction accompanying strand displacement, under a condition where the double-stranded nucleic acid is unstable using the inner primer RA as an origin, such that a region F2c of the target template nucleic acid to be annealed by an inner primer FA constituted by regions F1c and F2, whereby region F2 anneals to region F2c on the double-stranded nucleic acid template that is capable of amplifying the template nucleic acid at a constant temperature when the released single strand intramolecularly anneals with itself b) annealing a outer primer F3 to the region F3c of the single strand displaced in the step a), which is placed in a condition such that it can undergo base pairing; c) carrying out the complementary strand synthesis using the outer primer F3 as a synthesis origin, whereby the extended product synthesized using the inner primer FA as the origin is displaced and released as a single strand; and d) using the single strand as a template the inner primer RA and the outer primer R3, whereby region R2 anneals to region R2c, and R3 anneals to region R3c in the single strand displaced in step c) and initiate complementary strand synthesis.