Disclosed is a process for preparing a compound of the following formula (2): including the steps of reacting a compound of the following formula (4): with trityl chloride to prepare trityloxy-acetic acid ethyl ester of the following formula (8): reacting the compound of formula (8) with ethyl magnesium halide to prepare 1-trityloxymethyl-cyclopropanol of the following formula (9): combining the 1-trityloxymethyl-cyclopropanol of formula (9) with diisopropylbromo-methylphosphonate in a solvent in the presence of a base to prepare (1-trityloxymethyl-cyclopropoxymethyl)-phosphonic acid diisopropyl ester of the following formula (10): as a solid form, and converting the trityl group of the compound of formula (10) into a hydroxyl group.