The present invention relates to a liquid crystal aligning agent which contains a polymer that has a site having an isocyanate group and/or a blocked isocyanate group, a site having a photoreactive group having photoalignment, and a site having at least one functional group selected from an amino group and a hydroxyl group in each molecule. The present invention provides a liquid crystal display element which enables baking at low temperatures during the formation of a liquid crystal alignment film by a photoalignment method, the liquid crystal alignment film being able to be imparted with alignment regulating property and pretilt angle developing property.