1. An aromatic amino acid derivative represented by the formula (I) or its pharmacologically acceptable salt: ##STR00001## wherein, R.sup.1 is a hydrogen atom or an amino-protecting group, R.sup.2 is a halogen atom or an alkyl, aralkyl or aryl group, R.sup.3 is {circle around (1)} a hydrogen atom, {circle around (2)} an aroylamino group, {circle around (3)} a phenyl group substituted with lower alkyl, phenyl, phenoxy, etc. {circle around (4)} a naphthyl or tetrahydronaphthyl group optionally substituted with hydroxy, lower alkoxy or di(lower)alkylamino, {circle around (5)} an unsaturated mono-cyclic heterocyclic group containing N, O and/or S substituted with lower alkyl, phenyl, naphthyl or tetrahydroquinolyl, {circle around (6)} an unsaturated or partially saturated condensed heterocyclic group containing N, O and/or S, optionally substituted with oxo, carboxy, amino, lower alkyl, etc.; X is a halogen atom, an alkyl group or an alkoxy group; Y is oxygen atom or nitrogen atom; l is 0 or 1; m is 0, 1 or 2; n is an integer of 0-5. This compound can inhibit a transporter (LAT1) of essential amino acid which is one of main nutrition for cancer cells and accordingly cause drain of the essential amino acid on the cancer cells and finally can prohibit the multiplication of cancer cells.