A sample which contains protein is stably maintained in a liquid state during electrophoresis. Electrophoresis chip 1 includes substrate 2, channels 5a to 5d which is provided on surface 3 of substrate 2 and which has openings 4a to 4d at the top thereof, wherein a sample solvent is adapted to be supplied to the channel, and evaporation inhibitor reservoirs 8a, 8b for storing an evaporation inhibitor for the sample solvent, the reservoir being provided independently of channel 5a to 5d and being spatially connected to opening 4a to 4d of channel 5a to 5d.