To provide an electrophoresis method and an electrophoresis device which can reduce difficulty in operation while implementing sufficient staining. An electrophoresis device includes a temperature gradient tank, a dispenser, a holder storage cabinet, a photographing unit, a PCR device, a chip rack, a chip disposal box, a DC power unit, a control unit, an arm, and a liquid feeder. A holder and a cassette removably attached to the holder are put on the temperature gradient tank. The control unit controls a carrying device, the arm, the liquid feeder, the temperature gradient tank, an excitation light source and a camera in the photographing unit, and the DC power unit. The control unit prestores a program for executing the control operation in its internal memory.