a rare earth metal extractant containing , as the extractant component , dialkyldiglycol amide acid which is excellent in breaking down light rare earth elements is reacted in diglycolic acid and an esterification agent at a reaction temperature of 70 ° c . or more and for a reaction time of one hour or more such that the mol ratio of y / x is 2 . 5 or more , and is subjected to vacuum concentration . subsequently , a reaction intermediate product is obtained by removing unreacted products and reaction residue , and an aprotic polar solvent is added as the reaction solvent . then , the reaction intermediate product is reacted with dialkyl amine such that the mol ratio of z / x is 0 . 9 or more and the aprotic polar solvent is removed . as a consequence , a rare earth metal extractant is efficiently synthesized at a low cost and at a high yield without having to use expensive diglycolic acid anhydride and harmful dichloromethane .