an apparatus for conducting electrophoresis is fabricated by use of an electrophoresis sheet composed of two sheet members consisting of a non - conductive organic polymer film and disposed to stand facing each other , spacers having predetermined thicknesses disposed between the two sheet members at right and left edge portions , and an electrophoresis gel membrane of a uniform thickness grasped between the two sheet members . the apparatus is provided with a pair of flat plate - like supporting members for supporting the electrophoresis sheet by sandwiching it therebetween , and a spacer disposed between the electrophoresis sheet and at least one of the flat plate - like supporting members , and contacting edge portions of the electrophoresis sheet .