A method measuring a body fat by using a body fat measurement device including an optical detector and at least two light sources, the method including: detecting an optical signal which is scattered by a biological tissue by the optical detector, and measuring a first optical signal intensity and a second optical signal intensity calculating a slope the first optical signal intensity and the second optical signal intensity by using a distance between a first light source unit and a second light source unit, and a difference between the first optical signal intensity and the second optical signal intensity, the first optical signal intensity corresponding to the first light source unit and the second optical signal intensity corresponding to the second light source unit and measuring a thickness of body fat of the biological tissue from the calculated slope.
