It is an object to provide a nucleoside analog that can produce an oligonucleotide analog in which the two properties of chemical and biological stability, and the ability to form double strands, are excellent, and an oligonucleotide analog that includes that nucleoside analog. This is achieved by a nucleoside analog or salt thereof represented by Formula (I) below, in which, in Formula (I), R.sup.1 is any group selected from the group consisting of the group of Formula (1), the group of Formula (2), the group of Formula (3), the group of Formula (4), the group of Formula (5), the group of Formula (6), the group of Formula (7), the group of Formula (8), and any of these groups whose functional group has been protected by a protecting group, and k, l, m, and n are each independently an integer from 1 to 10.