Ultrasound diagnostic device and ultrasound diagnostic method

[Problem] To accurately detect the shape of cartilage, and to derive information relating to said cartilage on the basis of accurately detected echoes from the cartilage. [Solution] This ultrasound diagnostic device is provided with an ultrasound transmitting unit (4b) and an ultrasound receiving unit (4b), a low frequency component extraction unit (19) and a derivation unit (20). In a state in which the wave transmitting/receiving surface, where the ultrasound waves are sent and received, is positioned fixed relative to the cartilage (52), the ultrasound transmitting unit (4b) transmits ultrasound waves at the cartilage (52) in multiple bending states in which a second bone (55) is bent at different angles to a first bone (51). The ultrasound receiving unit (4b) receives an echo signal in each frame in each of the multiple bending states. From the echo signal, the low frequency component extraction unit (19) extracts low-frequency echo data, which is echo data of a frequency component lower than a prescribed frequency for the frame direction. The derivation unit (20) derives information relating to the cartilage on the basis of the low-frequency echo data.