A telomerase-inhibiting ENA oligonucleotide compound represented by a formula: E1-B1-B2-B3-B4-E2 (I), wherein E1 represents a group represented by the formula R1-; E2 represents a group represented by the formula -B7-R2; B4, B5, and B8 are identical or different, and each represents T.sup.p; B1, B2, B3, and B12 are identical or different, and each represents G.sup.p; B16 represents C.sup.p; and B6, B10, B14, and B18 are identical or different, and each represents A.sup.p, or a pharmacologically acceptable salt thereof for treating diseases in which telomerase is involved, such as cancer.