A radiation protection device (14) and a bone densitometer (10) using same. The radiation protection device (14) comprises: a housing (100) having a first plate (110) and a second plate (120) which are opposite to each other, a sidewall (130), and an accommodating cavity (140), wherein the first plate (110) and the second plate (120) are respectively provided with first and second insertion holes (112, 122) facing each other, so that an arm or a leg can sequentially pass through the first and second insertion holes (112, 122) and an aperture adjusting member (200) comprising multiple radiation protection plates (210) provided within the accommodating cavity (140), wherein the multiple radiation protection plates (210) can move towards or away from the central line of the second insertion hole (122), thereby switching between an initial state and a working state, when being in the initial state, the multiple radiation protection plates (210) enclose to form an initial hole (212), the aperture of which is greater than or equal to that of the second insertion hole (122), and when being in the working state, the multiple radiation protection plates (210) enclose to form an adaptation hole (214), wherein the aperture of the adaptation hole (214) is smaller than that of the second insertion hole (122), and front projections of the multiple radiation protection plates (210) on the second plate (120) are complete rings. The radiation protection device (14) has a good radiation protection effect.La présente invention concerne un dispositif de protection contre les rayonnements (14) et un ostéodensitomètre (10) lutilisant. Le dispositif de protection contre les rayonnements (14) comprend : un boîtier (100) comportant une première plaque (110) et une deuxième plaque (120) qui sont opposées lune à lautre, une paroi latérale (130), et une cavité de réception (140), la première plaque (110) et la deuxième plaque (120) comportant respectivement des premier et deuxième trous dinser
