A method for detecting a single-stranded RNA virus in a sample, the method comprising: bringing a primer set into contact with a sample to perform a reverse transcription loop-mediated isothermal amplification reaction, wherein the primer set is designed based on a nucleotide sequence of a target RNA of a single-stranded RNA virus and a nucleotide sequence of a nucleic acid complementary to the target RNA, wherein when the single-stranded RNA virus is a plus-strand single-stranded RNA virus, the target RNA comprises arbitrary regions F3, F2, F1, B1c, B2c, and B3c in this order in a direction from a 5' terminal to a 3' terminal, and the nucleic acid complementary to the target RNA comprises arbitrary regions F3c, F2c, F1c, B1, B2, and B3 in this order in a direction from a 3' terminal to a 5' terminal, wherein when the single-stranded RNA virus is a minus-strand single-stranded RNA virus, the target RNA comprises the arbitrary regions F3c, F2c, F1c, B1, B2, and B3 in this order in a direction from the 3' terminal to the 5' terminal, and the nucleic acid complementary to the target RNA comprises the arbitrary regions F3, F2, F1, B1c, B2c, and B3c in this order in a direction from the 5' terminal to the 3' terminal, wherein the regions F3, F2, F1, B1c, B2c, and B3c are respectively complementary to the regions F3c, F2c, F1c, B1, B2, and B3, wherein the primer set comprises following (i) to (v): (i) an FIP primer having the same nucleotide sequence as the region F1c at a 5' terminal and having the same nucleotide sequence as the region F2 at a 3' terminal; (ii) a BIP primer having the same nucleotide sequence as the region B1c at a 5' terminal and having the same nucleotide sequence as the region B2 at a 3' terminal; (iii) an F3 primer which is an outer primer having the same nucleotide sequence as the region F3; (iv) a B3 primer which is an outer primer having the same nucleotide sequence as the region B3; and (v) one or more additional outer primers, each additional outer primer having the same nucleotide sequence as an arbitrary region present on the 5' terminal side from the region B3 or the region F3 in the nucleic acid complementary to the target RNA, and wherein uracil that may be present in the nucleotide sequences of the FIP primer, the BIP primer, the F3 primer, the B3 primer, and the one or more additional outer primers may be substituted with thymine. bringing a primer set into contact with a sample to perform a reverse transcription loop-mediated isothermal amplification reaction, wherein the primer set is designed based on a nucleotide sequence of a target RNA of a single-stranded RNA virus and a nucleotide sequence of a nucleic acid complementary to the target RNA, wherein when the single-stranded RNA virus is a plus-strand single-stranded RNA virus, the target RNA comprises arbitrary regions F3, F2, F1, B1c, B2c, and B3c in this order in a direction from a 5' terminal to a 3' terminal, and the nucleic acid complementary to the target RNA comprises arbitrary regions F3c, F2c, F1c, B1, B2, and B3 in this order in a direction from a 3' terminal to a 5' terminal, wherein when the single-stranded RNA virus is a minus-strand single-stranded RNA virus, the target RNA comprises the arbitrary regions F3c, F2c, F1c, B1, B2, and B3 in this order in a direction from the 3' terminal to the 5' terminal, and the nucleic acid complementary to the target RNA comprises the arbitrary regions F3, F2, F1, B1c, B2c, and B3c in this order in a direction from the 5' terminal to the 3' terminal, wherein the regions F3, F2, F1, B1c, B2c, and B3c are respectively complementary to the regions F3c, F2c, F1c, B1, B2, and B3, wherein the primer set comprises following (i) to (v): (i) an FIP primer having the same nucleotide sequence as the region F1c at a 5' terminal and having the same nucleotide sequence as the region F2 at a 3' terminal; (ii) a BIP primer having the same nucleotide sequence as the region B1c at a 5' terminal and having the same nucleotide sequence as the region B2 at a 3' terminal; (iii) an F3 primer which is an outer primer having the same nucleotide sequence as the region F3; (iv) a B3 primer which is an outer primer having the same nucleotide sequence as the region B3; and (v) one or more additional outer primers, each additional outer primer having the same nucleotide sequence as an arbitrary region present on the 5' terminal side from the region B3 or the region F3 in the nucleic acid complementary to the target RNA, and (i) an FIP primer having the same nucleotide sequence as the region F1c at a 5' terminal and having the same nucleotide sequence as the region F2 at a 3' terminal; (ii) a BIP primer having the same nucleotide sequence as the region B1c at a 5' terminal and having the same nucleotide sequence as the region B2 at a 3' terminal; (iii) an F3 primer which is an outer primer having the same nucleotide sequence as the region F3; (iv) a B3 primer which is an outer primer having the same nucleotide sequence as the region B3; and (v) one or more additional outer primers, each additional outer primer having the same nucleotide sequence as an arbitrary region present on the 5' terminal side from the region B3 or the region F3 in the nucleic acid complementary to the target RNA, and wherein uracil that may be present in the nucleotide sequences of the FIP primer, the BIP primer, the F3 primer, the B3 primer, and the one or more additional outer primers may be substituted with thymine.