Carbazole polymer and organic electroluminescent element using same

A polymer containing a structural unit represented by formula (A). In formula (A), each P represents a group represented by formula (P). L represents a linking group. a represents an integer between 2 and 5, inclusive, and b represents an integer between 0 and 5, inclusive. In formula (P), each A represents a nitrogen atom or CR. X represents a single bond, O, S, C(R) 2 , or NR. Each R independently represents a hydrogen atom, a substituted or unsubstituted C1-20 alkyl group and the like, or a single bond used in the bond to another P or L. However, at least one R in (P)a is represented by one of formulas (3)-(7).