[Problem] To non-invasively and accurately detect a boundary surface between soft tissue and cartilage. [Solution] A device (10) for detecting a soft tissue/cartilage boundary surface is provided with a transmission controller (12), an echo signal receiver (13), a data analyzer (14), and a probe (100). The transmission controller (12), probe (100) and echo signal receiver (13) each acquire a plurality of sweeps of echo data in a state where the position of the probe (100) is varied between a first state and a second state. The data analyzer (14) runs correlation processing on an echo data group (DZT1) of a region of interest in a first echo data group (SW[T1]) of the first state, and an echo data group (DZT2) of a predetermined region in a second echo data group (SW[T2]) of the second state. In the data analyzer (14), relative positional changes of each of the regions between the first state and the second state with respect to the probe (100) are detected from the correlation processing result, and a determination between soft tissue and cartilage is made from the relative positional changes.
