A compound represented by the following formula (I) is used as a xanthine oxidase inhibitor: in which R
1
is phenyl or pyridyl each optionally having, as a substituent, C
1-8
alkyl, C
1-8
haloalkyl, C
1-8
alkoxy, carboxyl, halogeno, hydroxyl, nitro, cyano, amino, etc.; R
2
is cyano, nitro, etc.; X is oxygen, sulfur, etc.; and Y is sulfur, NH, etc.