An image processing device comprising: a storage unit configured to store therein image data on time-series computed tomography, CT, images in a plurality of frames of an organ of a subject captured after a contrast medium has been administered; a unit configured to determine an intra-organ pixel position, which is a position of a pixel in a region of the organ; a unit configured to determine a change-over-time of a CT value of the pixel at the intra-organ pixel position, based on image data on the time series CT images in the plurality of frames; and characterised by further comprising a unit configured to determine, as an upper limit frame, a predetermined frame in the plurality of frames after a sharp rise in the CT value in the change-over-time, the predetermined frame being a frame before a frame from which a maximum value of the CT value or a first peak value of the CT value in the change-over-time is detected; and a unit configured to determine an arrival time at which the contrast medium has arrived at the organ at the intra-organ pixel position, and a base value, which is a CT value, based on the change-over-time before the upper limit frame using a function and/or straight line linear approximation, the base value for serving as a baseline of a change in the CT value of the pixel at the intra-organ pixel position before the upper limit frame, the arrival time being a time at which the CT value starts to sharply rise in response to an arrival of the contrast medium at the organ. a storage unit configured to store therein image data on time-series computed tomography, CT, images in a plurality of frames of an organ of a subject captured after a contrast medium has been administered; a unit configured to determine an intra-organ pixel position, which is a position of a pixel in a region of the organ; a unit configured to determine a change-over-time of a CT value of the pixel at the intra-organ pixel position, based on image data on the time series CT images in the plurality of frames; and characterised by further comprising a unit configured to determine, as an upper limit frame, a predetermined frame in the plurality of frames after a sharp rise in the CT value in the change-over-time, the predetermined frame being a frame before a frame from which a maximum value of the CT value or a first peak value of the CT value in the change-over-time is detected; and a unit configured to determine an arrival time at which the contrast medium has arrived at the organ at the intra-organ pixel position, and a base value, which is a CT value, based on the change-over-time before the upper limit frame using a function and/or straight line linear approximation, the base value for serving as a baseline of a change in the CT value of the pixel at the intra-organ pixel position before the upper limit frame, the arrival time being a time at which the CT value starts to sharply rise in response to an arrival of the contrast medium at the organ. a unit configured to determine, as an upper limit frame, a predetermined frame in the plurality of frames after a sharp rise in the CT value in the change-over-time, the predetermined frame being a frame before a frame from which a maximum value of the CT value or a first peak value of the CT value in the change-over-time is detected; and a unit configured to determine an arrival time at which the contrast medium has arrived at the organ at the intra-organ pixel position, and a base value, which is a CT value, based on the change-over-time before the upper limit frame using a function and/or straight line linear approximation, the base value for serving as a baseline of a change in the CT value of the pixel at the intra-organ pixel position before the upper limit frame, the arrival time being a time at which the CT value starts to sharply rise in response to an arrival of the contrast medium at the organ.