An apparatus and system for quantitatively calculating bone density using an X-ray image of a photographed bone part, in particular alveolar bone, and an imaging aid for performing X-ray imaging of alveolar bone accurately and easily.The bone density measuring apparatus of the present invention comprises an image display unit for displaying an X-ray image of a photographed bone and a reference body on the same screen, and a reference body concentration for measuring the density of the X-ray image of the displayed reference body. The bone portion by comparing the X-ray image density of the bone portion with the X-ray image density of the reference body and the bone portion density measurement portion for measuring the density of the displayed X-ray image of the bone portion And a bone density calculation unit for calculating the bone density of the bone.
