To provide a resist polymer comprising, as a structural unit, an acid-decomposable unit having a structure represented by formula (1) or (2) which exhibits a small line edge roughness and produces little defects in DUV excimer laser lithography or the like. In formulas (1) and (2), n represents an integer of 2 to 24; J represents a single bond or a divalent hydrocarbon group which may have a substituent/heteroatom when n=2, or represents an n-valent hydrocarbon group which may have a substituent/heteroatom when n≧3; E represents a residue of a polymerization terminator, a chain transfer agent or a polymerization initiator; K1 and K2 each represent at least one selected from alkylene, cycloalkylene, oxyalkylene, arylene, a divalent thiazoline ring, a divalent oxazoline ring and a divalent imidazoline ring; L1 and L2 each represent at least one selected from —C(O)O—, —C(O)— and —OC(O)—; M1, M2 and M3 each represent at least one selected from alkylene, cycloalkylene, oxyalkylene and arylene; Y, Y1 and Y2 each represent an acid-decomposable linkage; k1, k2, l1, l2, m1, m2, and m3 each represent 0 or 1; and R1 represents H or a methyl group.