A radiation detector using gas amplification, includes: an insulator having a first surface and a second surface positioned at a back surface side of the first surface; a first electrode layer that is provided on the first surface of the insulator and has a circular opening portion; a pixel electrode positioned inside the opening portion; a second electrode layer provided on the second surface of the insulator; and a via hole conductor that has one end surface thereof bonded to the second electrode layer through the interior of the insulator and has the other end surface thereof bonded to the pixel electrode, in which at least a part of the other end surface side of the via hole conductor exhibits a column or truncated cone shape and an outer diameter of the via hole conductor becomes smallest at the one end surface.