An electrophoretic medium best suited as a separation medium is composed of a gel solution and contains a water-soluble polymer and permits great improvement of the enzymic protein recovery character. A gel holder is provided with stopper members and thus can hold even a soft or slippery while maintaining a fixed shape thereof, thus permitting reliable separation and purification of an intended substance without possibility of denaturing of the substance. A slab type electrophoretic apparatus permits automatic detection of the electrophoretic state of a sample and automatic completion of the electrophoresis under optimum conditions without setting measurement condition, permits continuous measurement of the buffer solution temperature, which is important for obtaining an electrophoretic condition for maintaining the enzymic function, and permits separation and purification of a large quantity of an enzyme or like physiologically active substance in a very simple operation. An electrophoretic gel cutter cuts even large size electrophoretic gels vary accurately and safely to desired sizes and particularly cuts a soft and readily deformable electrophoretic gel of polyacrylamide or the like in a pressurized state, thus permitting accurate and safe cutting of the polyacrylamide gel, which has been very difficult to cut, without causing damage to the gel.