By without X-ray irradiation for the focus position detection can be accurately estimated amount of movement of the focal position, to change the X-ray field, without causing delays photographing timing, due to the focus shift In order to eliminate image quality deterioration such as reduction in the quantitative and the occurrence of artifacts can be suppressed, and the X-ray generator 100, an X-ray detection unit 104, an X-ray collimator means 303, X-ray CT apparatus, reconstruction processing means 105, and the irradiation field changing drive means 200,301,302 for controlling movement of at least one of the X-ray collimator means 303 and the X-ray detecting means and the X-ray generator 100, to estimate the focal position of the X-ray generation means in the estimated time ( calculates the amount of movement of the irradiation field changing drive means required for S2, S4), using the estimation results, to maintain a constant X-ray incident position in the X-ray detection means and (S6) movement amount calculating means 105, I include a. When the predetermined time has elapsed from the time that was estimated focus position in the most recent past, or if the input of the photographing start instruction signal is, performs the calculation of the amount of movement the movement amount calculating means (S8), By X-ray irradiation or the next time estimate controls movement according to the moving amount of the irradiation field changing drive means, (S9).焦点位置検出のためのX線照射を行わずに、焦点位置の移動量を精度よく推定して、X線照射野を変更することで、撮影タイミングの遅延を生じることなく、焦点移動に起因するアーチファクトの発生や定量性の低下などの画質劣化を除去、抑制するために、X線CT装置は、X線発生手段100と、X線検出手段104と、X線コリメータ手段303と、再構成処理手段105と、X線発生手段100とX線検出手段とX線コリメータ手段303の少なくとも1つを制御移動する照射野変更駆動手段200,301,302と、推定時刻におけるX線発生手段の焦点位置を推定し(S2,S4)、その推定結果を用いて、X線検出手段におけるX線入射位置を一定に保つために必要な照射野変更駆動手段の移動量を算出する(S6)移動量算出手段105と、を備える。そして、直近の過去において焦点位置の推定を行った時刻から所定時間が経過した場合、又は撮影開始指示信号の入力がされた場合に、移動量算出手段は移動量の算出を行い(S8)、照射野変更駆動手段は、次の推定時刻又はX線照射までに、移動量に応じた制御移動を行う(S9)。
