an electrophoresis apparatus comprises a gel sheet device composed of spacers disposed between two films at side edges thereof , a gel membrane provided within a space formed between the two films by the spacers , and sample - pouring portions provided near an upper edge of the gel membrane . two supporting members hold the gel sheet device therebetween , and a gap - forming member contacts edges of at least one surface of the gel sheet device . each sample - pouring portion is adapted to sample pouring into a space formed by the films , a shark &# 39 ; s teeth comb , and the upper edge face of the gel membrane . the gap - forming member remote from an upper buffer solution vessel is provided such that an inner edge of a gap - forming member portion contacting the upper portion of the gel sheet device coincides with the upper edge face of the gel membrane , or the extent of overlapping of the gap - forming member portion upon the gel membrane is 5 mm or less .