As a result of extensive studies on NAD(P)H oxidase inhibitors, the present inventors found that a quinolone derivative having, at the 2-position, an alkyl group substituted with a heteroatom or the like has an excellent NAD(P)H oxidase inhibitory activity, and accomplished the present invention. The compound of the present invention has a reactive oxygen species production inhibitory activity based on the NAD(P)H oxidase inhibitory activity, and therefore can be used as an agent for preventing and/or treating diabetes, impaired glucose tolerance, hyperlipidemia, fatty liver, diabetetic complications and the like.