1. A portable radiographic imaging apparatus comprising: an image output unit which detects a radiation which penetrates an object to be imaged and is irradiated onto a surface of a casing of the portable radiographic imaging apparatus, and outputs data of a radiographic image which represents a distribution of an amount of irradiated radiation; a first storage unit which stores the data of the radiographic image output from the image output unit; a display unit which displays an image; and a display control unit that causes the display unit to display a previously captured radiographic image associated with a current imaging, before the object to be imaged is imaged, after receiving a request to display the previously captured radiographic image, wherein data of previously captured radiographic images is stored in the first storage unit, and wherein the display control unit searches the data of the previously captured radiographic images stored in the first storage unit for the data of the previously captured radiographic image associated with the current imaging, reads out from the first storage unit the data of the previously captured radiographic image extracted by the searching, and causes the display unit to display the read out data as the previously captured radiographic image associated with the current imaging.