Abstract: The present invention relates to a polysubstituted imidazolo[4,5-c][1,2]thiazine derivative and a use of an agent comprising same as an active agent, which is useful for infectious diseases associated with vascular inflammation caused by HMGB1 protein activity. It has been found that the polysubstituted imidazolo[4,5-c][1,2]thiazine derivative of the present invention increases the sepsis survival rate as a result of searching for antiseptic effects through CLP-induced sepsis animal experiments. Accordingly, the agent comprising the polysubstituted imidazolo[4,5-c][1,2]thiazine derivative or a pharmaceutically acceptable salt thereof as an active agent may be advantageously used as a therapeutic agent for infectious diseases and vascular inflammatory diseases including sepsis caused by HMGB1 protein activity.