An electrophoresis plate has a plurality of separation channels provided inside a substrate. The separation channels are arranged along the surface of the substrate without intersecting each other, and the separation channels have openings on both ends on the substrate surface. When a voltage is applied between the two ends of the channel, a sample is separated by electrophoresis along the channel. The openings on one end are placed in a matrix pattern as sample inlet ports, and the pitch of that placement is set equal to the pitch of the wells of a sample plate containing the samples to be injected into the sample inlet ports. Since the pitch of the sample inlet ports pattern is equal to the pitch of the sample plate wells, sample injection can be performed quickly and conveniently even with a large number of separation channels.