A bone mineral density evaluation system for evaluating a bone mineral density from an X-ray picture of a mandible, said X-ray picture containing a picture of a specimen disposed beside said mandible, said system comprising: detecting means for detecting a brightness of said picture of said specimen; correcting means for correcting the brightness of said X-ray picture; and evaluating means for evaluating the bone mineral density on the basis of the corrected brightness of said X-ray picture as corrected by said correcting means; characterised in that: said evaluating means is adapted to make evaluation on the basis of the corrected brightness of a particular region (38, 254) of said mandible in said X-ray picture; said particular region includes a region corresponding to an alveolar bone portion around a first premolar; said detecting means is adapted to detect maximum and minimum values of a brightness of said picture of said specimen; and said correcting means is adapted to make said correction by determining a corrected brightness Y'[i,j] in accordance with the following expression, where Ybmax is the maximum brightness value, Ybmin is the minimum brightness value, Ysmax is the standard maximum value, Ysmin is the standard minimum value, and Y[i,j] is the brightness of said X-ray picture before the correction, where [i,j] is the coordinate of each of the pixels forming said X-ray picture: Yʹ i j = Δ Y i j + Ys min where Δ Y i j = Y i j - Yb min Yb max - Yb min ⋅ Ys max - Ys min. detecting means for detecting a brightness of said picture of said specimen; correcting means for correcting the brightness of said X-ray picture; and evaluating means for evaluating the bone mineral density on the basis of the corrected brightness of said X-ray picture as corrected by said correcting means; characterised in that: said evaluating means is adapted to make evaluation on the basis of the corrected brightness of a particular region (38, 254) of said mandible in said X-ray picture; said particular region includes a region corresponding to an alveolar bone portion around a first premolar; said detecting means is adapted to detect maximum and minimum values of a brightness of said picture of said specimen; and said correcting means is adapted to make said correction by determining a corrected brightness Y'[i,j] in accordance with the following expression, where Ybmax is the maximum brightness value, Ybmin is the minimum brightness value, Ysmax is the standard maximum value, Ysmin is the standard minimum value, and Y[i,j] is the brightness of said X-ray picture before the correction, where [i,j] is the coordinate of each of the pixels forming said X-ray picture: Yʹ i j = Δ Y i j + Ys min where Δ Y i j = Y i j - Yb min Yb max - Yb min ⋅ Ys max - Ys min. said evaluating means is adapted to make evaluation on the basis of the corrected brightness of a particular region (38, 254) of said mandible in said X-ray picture; said particular region includes a region corresponding to an alveolar bone portion around a first premolar; said detecting means is adapted to detect maximum and minimum values of a brightness of said picture of said specimen; and said correcting means is adapted to make said correction by determining a corrected brightness Y'[i,j] in accordance with the following expression, where Ybmax is the maximum brightness value, Ybmin is the minimum brightness value, Ysmax is the standard maximum value, Ysmin is the standard minimum value, and Y[i,j] is the brightness of said X-ray picture before the correction, where [i,j] is the coordinate of each of the pixels forming said X-ray picture: Yʹ i j = Δ Y i j + Ys min where Δ Y i j = Y i j - Yb min Yb max - Yb min ⋅ Ys max - Ys min.