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 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 at detectable levels within 15 minutes, wherein the nucleic acid amplification product comprises: the sequence of the first primer or the reverse complement thereof, the sequence of the second primer or the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer or the reverse complement thereof and the sequence of the second primer or 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 (b) detecting the nucleic acid amplification product. (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 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 at detectable levels within 15 minutes, wherein the nucleic acid amplification product comprises: the sequence of the first primer or the reverse complement thereof, the sequence of the second primer or the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer or the reverse complement thereof and the sequence of the second primer or 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 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 at detectable levels within 15 minutes, wherein the nucleic acid amplification product comprises: the sequence of the first primer or the reverse complement thereof, the sequence of the second primer or the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer or the reverse complement thereof and the sequence of the second primer or the reverse complement thereof, wherein the spacer sequence is 1 to 10 bases long; and the sequence of the first primer or the reverse complement thereof, the sequence of the second primer or the reverse complement thereof, and a spacer sequence flanked by the sequence of the first primer or the reverse complement thereof and the sequence of the second primer or the reverse complement thereof, wherein the spacer sequence is 1 to 10 bases long; and (b) detecting the nucleic acid amplification product.