A timing to acquire a still image signal is controlled such that a sum (Tst+Trd) of a storage period Tst and a readout period Trd for the still image signal is an integral multiple (Ts+Tr=Tck×n, where n is an integer of 2 or greater) of a cycle Tck of a moving image capturing mode, when a detector controller acquires the still image signal while acquiring a moving image signal from a radiation detector during the cycle Tck (Ts+Tr) of the moving image capturing mode.