Checking the fit between a prosthetic socket and a residual limb is important for functional prostheses. Designing a prosthetic socket using a CAD system and checking the above mentioned fit by analyzing the deformation and stress under the weight of an amputee requires a three-dimensional model of the residual limb that includes not only the surface, but also the fat, muscle and bone. An ultrasonic measurement system, including a probe that three-dimensionally measures the external surface shape and the shapes of internal tissues simultaneously was developed. The system uses wavelet analysis to define the positions of the boundaries between each tissue. A cone-shaped aluminum test object was measured using the system, which was shown to be capable of measuring radius with an error of 0.6mm and slope with an error of 6%. In addition, the lower legs were measured, and the surface, muscles and bone boundaries were defined by wavelet analysis. The results of these measurements were compared to MRI cross sectional data, and the average error for the leg surface, muscles and tibia were 1.7mm, 2.4mm and 1.9mm, respectively, for boundaries that were determined correctly.