The purpose of the present invention is to provide : a pharmaceutical composition that comprises the pyridylaminoacetic acid compound of the present invention, said pyridylaminoacetic acid compound being stable within the pharmaceutical composition; and a method for improving the stability of the pydridylaminoacetic acid compound within the pharmaceutical composition. The pharmaceutical composition comprises : (6{[4-(pyrazol-1-yl)benzyl](pyridine-3-ylsulfonyl)aminomethyl}pyridine-2-ylamino)isopropyl acetate or a salt thereof; and polyoxyethylene castor oil. The polyoxyethylene castor oil preferably comprises a polyoxyethylene castor oil selected from the group consisting of polyoxyl 5 castor oil, polyoxyl 9 castor oil, polyoxyl 15 castor oil, polyoxyl 35 castor oil, and polyoxyl 40 castor oil.