This invention relates to a technology for preventing leakage of liquid from gel (70). The electrode chip (10) comprises a cup-like support (20) including a cup part (210), and a sheet-like support (30) attached with an electrode layer (40). The gel (70) in the cup part (210) delivers liquid (700) containing water confined at the time of crosslinking. The liquid (700) moves by capillarity from the gel (70) side through a narrow gap between the outer flange (220) of the cup-like support (20) and the outside part (310o) of the sheet-like support (30) in a direction away from the gel (70). Since a groove (80) exists in the vicinity of the cup part (210) and the gap is large at that part, capillarity is broken thereat.