The object of the present invention is to provide an antibacterial agent which has an improved antibacterial effect and a wider antibacterial spectrum than conventional antibacterial agents, and which is highly safe to human and the environment. This object is achieved with a novel substance 9-(1',5'-dimethyl-1'-vinyl-4'-hexenyl)-4-hydroxy-7H-furo[3,2-.g- amma.][1]benzopyran-7-one and an antibacterial agent comprising thereof.