PROBLEM TO BE SOLVED: To calculate an EI having high reliability without taking much time and trouble.SOLUTION: An electronic cassette 13 includes a lighting field setting part 56 for automatically setting a lighting field being an area of a detection pixel 41b for detecting dose for an AEC during irradiation of X-ray on the basis of a dose detection signal from the detection pixel 41b. A console 14 acquires lighting field information set by the lighting field setting part 56 and an X-ray image with an information acquisition part 82. A calculation part 80 determines the lighting field set by the lighting field setting part 56 as a calculation area for calculating an EI, extracts a representative value V from a pixel value of a pixel 41 existing in the lighting field, and calculates an EI on the basis of the extracted representative value V.【課題】時間や手間を掛けずに信頼性の高いＥＩを算出する。【解決手段】電子カセッテ１３には、ＡＥＣのために線量を検出する検出画素４１ｂの領域である採光野を、検出画素４１ｂからの線量検出信号に基づきＸ線の照射中に自動的に設定する採光野設定部５６が設けられている。コンソール１４は、採光野設定部５６で設定された採光野情報とＸ線画像を情報取得部８２で取得する。算出部８０は、採光野設定部５６で設定された採光野をＥＩを算出する算出領域と定め、採光野に存在する画素４１の画素値から代表値Ｖを抽出し、抽出した代表値Ｖに基づきＥＩを算出する。【選択図】図１２
