In a radiation detector according to this invention, a portion of a semiconductor, located in a connection of a common electrode to a lead wire, is dented in a recess form from other portions of a semiconductor, in a range short of a radiation detection effective area. An insulating seat is disposed to fill the portion located in the connection. The common electrode is formed to cover at least part of the seat. The lead wire is connected to a portion of the incidence surface of the common electrode located on the seat. Thus, the detector can avoid performance degradation resulting from connection of the lead wire to the common electrode, and avoid problems of heat deformation stress and radiation attenuation.