There are provided an apparatus capable of complying with arbitrary data acquisition period (frame rate) change instruction without increasing load and cost, and a method and a system for controlling such an apparatus. To realize this, in the present invention, there are included an area sensor for reading out an electric signal accumulated in a plurality of pixels arranged in a matrix, line by line, and a control unit for controlling the area sensor. The area sensor operates in a first operation for deriving radiation image data by reading during irradiation with radiation, and a second operation for deriving the radiation image data by reading during non-irradiation with radiation, alternately. The control unit switches a period for deriving the radiation image data during a time period from an end of the reading in the first operation until an end of the reading in the second operation.