PROBLEM TO BE SOLVED: To provide a natural organic compound which has an effect of inhibiting precursor fat cells from differentiating to fat cells and an effect of reducing fat droplets in fat cells and a medical drug containing the natural organic compound as an effective ingredient.SOLUTION: A novel natural organic compound of chemical formula (1) was isolated from a cyanobacterium collected at Maibara, Ishigaki-Jima, Okinawa Prefecture and has an activity of inhibiting precursor fat cells from differentiating to fat cells and an activity of reducing fat droplets in fat cells. An antiobestic drug contains the compound as an effective ingredient and reduces cell droplets in fat cells.