A portable radiation imaging apparatus including: a detection section which includes a plurality of radiation detection elements for accumulating electric charges corresponding to a radiation amount, the radiation detection elements being two-dimensionally arranged; and a control section which controls accumulation of the electric charges in the radiation detection elements and reading of the accumulated electric charges from the radiation detection elements and generates a plurality of frame images of a subject, the electric charges to be accumulated corresponding to the radiation amount of radiation emitted in a pulsed manner by a radiation source and transmitted through the subject, wherein the control section adjusts a synchronization timing between the radiation source and the detection section by using a waveform of radiation emitted by the radiation source, the waveform being obtained by reading electric charges from at least a part of the plurality of radiation detection elements.