Opposing with x-ray source and this x-ray source which produce the x-ray, it outputs as the graphics data being the x-ray diagnostic device which has with the x-ray detector where it is arranged, detects the transmitted x-ray of the suffering inspection body and, The suffering inspection body picture area calculation expedient which calculates the area of the suffering inspection body territory which is occupied in the graphics data on the basis of the distance to the aforementioned x-ray detector, it should detect with the aforementioned x-ray detector directly by x-ray which calculates the pixel value which directly corresponds to the x-ray which quantity quantitative calculation expedient and the aforementioned histogram compilation expedient were drawn up the histogram and the description above which directly by x-ray quantitative calculation expedient was calculated on the basis of the pixel value which from histogram compilation expedient and the lighting x-ray quantity and the aforementioned x-ray source which of the x-ray source which is stipulated under lighting conditions of the x-ray draw up the histogram of the pixel value in the graphics data which is output from the aforementioned x-ray detector,With, the aforementioned lighting x-ray quantity, from the area, and the aforementioned x-ray source of the aforementioned suffering inspection body picture territory on the basis of the distance to the x-ray detector, the area dose operational expedient which calculates the being bombed area dose of the suffering inspection body is had.X線を照射するX線源と、このX線源と対向して配置され、被検体の透過X線を検出して画像データとして出力するX線検出器とを備えるX線診断装置であって、前記X線検出器から出力される画像データにおける画素値のヒストグラムを作成するヒストグラム作成手段と、X線の照射条件で規定されるX線源の照射X線量及び前記X線源から前記X線検出器までの距離に基づいて、前記X線検出器で検出されるべき直接X線量に対応する画素値を計算する直接X線量計算手段と、前記ヒストグラム作成手段によって作成されたヒストグラム及び前記直接X線量計算手段によって計算された画素値に基づいて、画像データ中に占める被検体領域の面積を算出する被検体画像面積算出手段と、前記照射X線量、前記被検体画像領域の面積、及び前記X線源からX線検出器までの距離に基づいて、被検体の被曝面積線量を演算する面積線量演算手段を備える。
