A first dimension electrophoresis apparatus of vertical type with a gel container 2 having a plurality of rectangular rod-shaped gel chambers is provided. The rod-type gels surrounded with non-conductive material plates are arranged in parallel, an upper open end of the gel container 2 is placed tightly into an upper buffer reservoir 4 and the lower open end thereof is placed tightly into a lower buffer reservoir 1. The gel container 2 and the main parts of the first buffer reservoir 4 and the lower buffer reservoir 1 are sunk in a cooling reservoir 5 filled with cooling liquid. The lower buffer reservoir has a panel portion 1b which is bent upward to penetrate the cooling reservoir. Outlet conductors thereof extend from each of the reservoirs and are insulated physically and electrically from the cooling liquid. As a result, the outer surface of the gel container can directly contact with the cooling liquid.