Quinolizinone compound and use thereof as HIV integrase inhibitor

A pharmaceutical agent having an anti-HIV action, particularly, a pharmaceutical agent having an integrase inhibitory action, is provided. The present invention relates to a quinolizinone compound represented by the following formula [I] wherein each symbol is as defined in the specification, a pharmaceutically acceptable salt thereof, and an anti-HIV agent containing same as an active ingredient. The compound of the present invention has an HIV integrase inhibitory action and is useful as an anti-HIV agent for the prophylaxis or therapy of AIDS. Moreover, by a combined use with other anti-HIV agents such as protease inhibitors, reverse transcriptase inhibitors and the like, the compounds can become a more effective anti-HIV agent. Since the compound has a high inhibitory activity specific for integrases, the compound can provide a safe pharmaceutical agent for human with a fewer side effects.