To provide a phase difference conditioner capable of conditioning the phase difference in the thickness of a coating film for optical compensation to a negative direction, further, to provide a coating film for optical compensation having the properties of ((nx+ny)/2-nz)×d<0, and to provide an optical element having the same properties without providing a troublesome film forming step or the like.

The phase difference conditioner for a cellulose N-substituted carbamate is composed of at least one selected from a carbamate, an N-substituted carbamate, urea and an N-substituted urea. The carbamate is a compound expressed by formula (I) (wherein, R1 is a 1 to 20C alkyl group, a 1 to 20C alkyl halide group, a 6 to 20C aryl group or a 7 to 20C aralkyl group) or the like. The N-substituted carbamate is a compound expressed by formula (VIII) (wherein, R27 is a 1 to 20C alkyl group or a 1 to 20C alkyl halide group) or the like. The urea and the N-substituted urea are a compound expressed by formula (XXX) (wherein, R142 and R 143 are the same or different, and are represented by a hydrogen atom, a 1 to 20C alkyl group or the like) or the like.