A cartridge detachably mountable to a main assembly of an image forming apparatus, the main assembly including a main assembly electrical contact, includes a roller including an electroconductive shaft, the roller being rotatable with the shaft; and a supporting member rotatably supporting the shaft and provided with a hole portion for exposing a part of a surface of a longitudinal end of the shaft to directly contact the part to the main assembly electrical contact and an end surface positioning portion for determining a position of the end surface with respect to a longitudinal direction of the shaft by contacting another part of the end surface.