A radiation imaging apparatus is capable of taking a moving picture by acquisition by a reading circuit of a plurality of radiation image signals on the basis of a plurality of successive times of irradiation of a radiation detector with radiation rays. The radiation detector has a two-dimensional array of pixels. In a period between a start of an n-th time of irradiation with radiation rays and a start of an (n+1)-th time of irradiation with radiation rays, where n is a natural number, a controller switches an operation status of an analog-to-digital converter that converts electric signals read by the reading circuit into digital signals so that power consumption of the analog-to-digital converter is reduced.