A portable detector panel includes an X-ray detector assembly having an X-ray detecting surface on its surface, a box-like case that houses the X-ray detector assembly therein and whose upper part that is opposite to the X-ray detecting surface is X-ray transmissive, and a spacer that supports the X-ray detector assembly housed in the case so as to be apart from the inner bottom wall of the case, wherein the spacer is arranged between the X-ray detector assembly and the inner bottom wall of the case, is made of a hard material, and has a flexible shape with respect to the movement of the X-ray detector assembly in the direction substantially parallel to the X-ray detecting surface.
