A control device of a radiation image capturing apparatus performs repeated reading of leak data prior to radiation image capturing operation and, when a threshold value has been exceeded by the leak data having been read out, said control device detects the start of irradiation. If there are periodic fluctuations in the leak data read out prior to radiation image capturing operation even though irradiation has not started, said control device determines whether or not a threshold value has been exceeded by a value obtained by subtracting a previously obtained fluctuation pattern of the leak data from the read-out leak data during a time period including at least a time period when the leak data fluctuates.
