To obtain the subject agent useful as a functional material for optical resolution of a carboxylic acid compound, etc., from inexpensive raw materials, by including a specific compound derivative of noncyclic saccharide.

This agent contains a compound derivative of a noncyclic saccharide in which a part of the hydroxyl groups of a compound of a noncyclic saccharide (e.g. maltose, etc.), having a skeleton structure comprising a D- glucopyranoside of formula I ((n) is ≥2) as a repeating unit is etherified and the rest if esterified. The derivative is obtained, for example, by dissolving the noncyclic saccharide in an anhydrous solvent, reacting the solution with an alkyl halide such as pentyl bromide or the like by adding an alkali hydroxide such as NaOH or the like and esterifying the reaction product with a carboxylic acid anhydride such as trifluoroacetic acid anhydride or the like. The derivative is preferably a compound of formula II (RO and R'CO2 are each an ether or ester substituent).