A resist polymer (Y′), which is used as a resist resin in DUV excimer laser lithography, electron beam lithography, and the like, contains a polymer (Y) comprising: a constituent unit (A) having a lactone skeleton; a constituent unit (B) having an acid-eliminable group; a constituent unit (C) having a hydrophilic group; and a constituent unit (E) having a structure represented by the following formula (1), wherein a content of the constituent unit (E) is 0.3 mol % or more based on the total number of the constituent units of the resist polymer (Y′): in the formula (1), L is a divalent linear, branched, or cyclic C1-20 hydrocarbon group which may have a substituent and/or a heteroatom; R11 is a g-valent linear, branched, or cyclic C1-20 hydrocarbon group which may have a substituent and/or a heteroatom; and g represents an integer of 1 to 24.