A method for determining the presence, absence or amount of a target nucleic acid sequence in a sample, the method comprising: (a) amplifying a target nucleic acid sequence comprising a first strand and a second strand complementary to each other in an isothermal amplification condition, wherein the amplifying comprises contacting a non-denatured nucleic acid comprising the target nucleic acid sequence with: i) a first primer and a second primer, wherein the first primer is capable of hybridizing to a sequence of the first strand of the target nucleic acid sequence, and the second primer is capable of hybridizing to a sequence of the second strand of the target nucleic acid sequence; and ii) an enzyme having a hyperthermophile polymerase activity, thereby generating a nucleic acid amplification product, wherein the nucleic acid amplification product comprises: the sequence of the first primer, and the reverse complement thereof, the sequence of the second primer, and the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer and the reverse complement thereof and the sequence of the second primer and the reverse complement thereof, wherein the spacer sequence is 1 to 10 bases long; and wherein the amplifying does not comprise using any enzyme other than the enzyme having a hyperthermophile polymerase activity, and the amplifying does not comprise denaturing the non-denatured nucleic acid; and (b) detecting the nucleic acid amplification product, wherein the detecting is performed in 10 minutes or less from the time the non-denatured nucleic acid is contacted with (a)(i) the first and second primers and (a)(ii) the enzyme having a hyperthermophile polymerase activity. (a) amplifying a target nucleic acid sequence comprising a first strand and a second strand complementary to each other in an isothermal amplification condition, wherein the amplifying comprises contacting a non-denatured nucleic acid comprising the target nucleic acid sequence with: i) a first primer and a second primer, wherein the first primer is capable of hybridizing to a sequence of the first strand of the target nucleic acid sequence, and the second primer is capable of hybridizing to a sequence of the second strand of the target nucleic acid sequence; and ii) an enzyme having a hyperthermophile polymerase activity, thereby generating a nucleic acid amplification product, wherein the nucleic acid amplification product comprises: the sequence of the first primer, and the reverse complement thereof, the sequence of the second primer, and the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer and the reverse complement thereof and the sequence of the second primer and the reverse complement thereof, wherein the spacer sequence is 1 to 10 bases long; and wherein the amplifying does not comprise using any enzyme other than the enzyme having a hyperthermophile polymerase activity, and the amplifying does not comprise denaturing the non-denatured nucleic acid; and i) a first primer and a second primer, wherein the first primer is capable of hybridizing to a sequence of the first strand of the target nucleic acid sequence, and the second primer is capable of hybridizing to a sequence of the second strand of the target nucleic acid sequence; and ii) an enzyme having a hyperthermophile polymerase activity, thereby generating a nucleic acid amplification product, wherein the nucleic acid amplification product comprises: the sequence of the first primer, and the reverse complement thereof, the sequence of the second primer, and the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer and the reverse complement thereof and the sequence of the second primer and the reverse complement thereof, wherein the spacer sequence is 1 to 10 bases long; and the sequence of the first primer, and the reverse complement thereof, the sequence of the second primer, and the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer and the reverse complement thereof and the sequence of the second primer and the reverse complement thereof, wherein the spacer sequence is 1 to 10 bases long; and (b) detecting the nucleic acid amplification product, wherein the detecting is performed in 10 minutes or less from the time the non-denatured nucleic acid is contacted with (a)(i) the first and second primers and (a)(ii) the enzyme having a hyperthermophile polymerase activity.