A radiation detector (RD1, RD2, RD3) comprising: a semiconductor substrate of a first conductivity type having first and second principal faces opposed to each other and generating carriers in response to incidence of radiation; a plurality of semiconductor regions (10, 11, 13) of a second conductivity type which are two-dimensionally arrayed on the first principal face side of the semiconductor substrate in the semiconductor substrate, which make junctions with the semiconductor substrate, and into which carriers generated in the semiconductor substrate flow; and a plurality of electrodes (21, 23) arranged corresponding to the respective semiconductor regions (10, 11, 13) of the second conductivity type on the first principal face side of the semiconductor substrate and joined to the corresponding semiconductor regions of the second conductivity type, wherein each of the plurality of semiconductor regions of the second conductivity type includes either a first semiconductor region or a second semiconductor region, wherein the plurality of first semiconductor regions forms a two-dimensional array and the plurality of second semiconductor regions forms a two-dimensional array, wherein the first semiconductor regions arrayed in a first direction in the two-dimensional array out of the plurality of first semiconductor regions are electrically connected to each other, and wherein the second semiconductor regions arrayed in a second direction intersecting with the first direction out of the plurality of second semiconductor regions are electrically connected to each other, characterized in that when viewed from a direction perpendicular to the first principal face, the plurality of electrodes (21, 23) cover the respective semiconductor regions of the second conductivity type so that outer edges thereof are located outside outer edges of the corresponding semiconductor regions (10, 11, 13) of the second conductivity type. a semiconductor substrate of a first conductivity type having first and second principal faces opposed to each other and generating carriers in response to incidence of radiation; a plurality of semiconductor regions (10, 11, 13) of a second conductivity type which are two-dimensionally arrayed on the first principal face side of the semiconductor substrate in the semiconductor substrate, which make junctions with the semiconductor substrate, and into which carriers generated in the semiconductor substrate flow; and a plurality of electrodes (21, 23) arranged corresponding to the respective semiconductor regions (10, 11, 13) of the second conductivity type on the first principal face side of the semiconductor substrate and joined to the corresponding semiconductor regions of the second conductivity type, wherein each of the plurality of semiconductor regions of the second conductivity type includes either a first semiconductor region or a second semiconductor region, wherein the plurality of first semiconductor regions forms a two-dimensional array and the plurality of second semiconductor regions forms a two-dimensional array, wherein the first semiconductor regions arrayed in a first direction in the two-dimensional array out of the plurality of first semiconductor regions are electrically connected to each other, and wherein the second semiconductor regions arrayed in a second direction intersecting with the first direction out of the plurality of second semiconductor regions are electrically connected to each other, characterized in that when viewed from a direction perpendicular to the first principal face, the plurality of electrodes (21, 23) cover the respective semiconductor regions of the second conductivity type so that outer edges thereof are located outside outer edges of the corresponding semiconductor regions (10, 11, 13) of the second conductivity type.