Provided is a feature for performing more accurate analysis in a sample separation adsorption method. A gel cassette (22) is provided with a separation medium (19) for separating out a sample by electrophoresis and discharging the sample, a first insulating portion (13a) and a second insulating portion (13b) sandwiching the separation medium, and warping prevention portions (20) that are inserted between the first insulating portion (13a) and the second insulating portion (13b), and that mitigate warping of the first insulating portion (13a) and the second insulating portion (13b).
