According to the present invention, a liquid crystal aligning agent is configured to contain a polymer [P] which has a partial structure represented by formula (1) and comprises a photo-alignment group. In formula (1), each of R1 and R2 independently represents a hydrogen atom, a halogen atom or a monovalent organic group having one or more carbon atoms; and each of X1 and X2 independently represents —OH, —NH2 or a monovalent organic group having one or more carbon atoms, provided that at least one of X1 and X2 represents “—OR3” or “—NR3R4” (wherein each of R3 and R4 independently represents a hydrogen atom or a monovalent organic group having one or more carbon atoms).