The radiation detection element comprising a semiconductor part having a plate shape, a first electrode that is disposed on a first surface being one surface of the semiconductor part and that collects charges generated by incidence of radiation in the semiconductor part, a second electrode that is disposed on a second surface being the other surface of the semiconductor part and that is applied with voltage needed for collecting the charges, and a heavily-doped layer that is disposed at a region of the second surface excluding an edge of the semiconductor part and is doped heavier than the semiconductor part with dopants for making a type of a semiconductor equal to that of the semiconductor part. The heavily-doped layer is on the second surface located at a position overlapped with the second electrode and is thicker than the second electrode.