A control unit controls a detector including a pixel array arranged in a matrix, a driving circuit that drives the pixel array by a changeable number of pixels, and a readout circuit that outputs an electrical signal from the pixel array. The control unit controls, with a change from a first image capturing operation for repeating a set of a first accumulation operation and a first image output operation a plurality of times at a first frame rate to a second image capturing operation for repeating a set of a second accumulation operation and a second image output operation a plurality of times at a second frame rate, so that the detector continuously repeats a set of the second accumulation operation and an initialization operation a plurality of times at the second frame rate in a period between the first image capturing operation and the second image capturing operation.
