A portable radiation image capturing apparatus is described. In the portable radiation image capturing apparatus multiple image capturing elements are two-dimensionally arranged, the apparatus is provided with a current detecting means for detecting a current flowing in the apparatus, a read-out circuit having a power supply mode in which the charge generated in each image capturing element can be read out and converted into an electric signal and a stand-by mode in which charge is not read out and power is consumed less than in the power supply mode, and a control means for causing the read-out circuit to change from the stand-by mode to the power supply mode when detecting start of irradiation with radiation on the basis of an increase in the current value detected by the current detecting means while the read-out circuit is in the stand-by mode.
