The present invention is to provide a medical composition for the treatment or prophylaxis of glaucoma which comprises a pyridylaminoacetic acid compound represented by the formula (1): wherein R 1 , R 2 and R 3 each independently represent a hydrogen atom or C 1 -C 6 alkyl group, Y represents a bicyclic heteroaromatic ring group which may be substituted by a group(s) selected from the group consisting of a halogen atom, C 1 -C 6 alkyl group, halogeno C 1 -C 6 alkyl group, C 1 -C 6 alkoxyl group, halogeno C 1 -C 6 alkoxyl group and C 1 -C 6 alkylthio group or a group -Q 1 -Q 2 wherein Q 1 represents an arylene group or 5- to 6-membered heteroarylene group, Q 2 represents an aromatic group or a 5- to 6-membered ring heterocyclic group each of which may be substituted by a group(s) selected from the group consisting of a halogen atom, hydroxyl group, C 1 -C 6 alkyl group, halogeno C 1 -C 6 alkyl group, C 1 -C 6 alkoxyl group and halogeno C 1 -C 6 alkoxyl group, Z represents an aromatic group or a 5- to 6-membered heteroaromatic ring group each of which may be substituted by a group(s) selected from the group consisting of a halogen atom, C 1 -C 6 alkyl group, halogeno C 1 -C 6 alkyl group, C 1 -C 6 alkoxyl group and halogeno C 1 -C 6 alkoxyl group, or a pharmaceutically acceptable salt thereof as an effective ingredient.
