[Problem] To accurate detect boundaries between soft tissue and cartilage non-invasively. [Solution] Echo data for first and second states are acquired (S101 and S102). On the basis of the echo data for the first and second states, echo data for a subchondral bone (911) in the first state and the second state are detected (S103). On the basis of the subchondral bone echo data for the first state and the second state, movement vectors for the subchondral bone echo data are detected (S104). On the basis of the movement vectors, alignment is performed between sample data for comparison of the echo data for the first state and the echo data for the second state (S105). Correlation coefficients for the echo data for the first state and the echo data for the second state, which are to be identical sample positions for comparison by way of alignment, are calculated (S106). Determinations are made of areas of high coefficients as cartilage and areas of low coefficients as soft tissue, and interfaces therebetween are
