Moreover, in the channel forming member 31 at the lower side, three through holes 23 a, 23 b, and 23 c which are extended from an area of the three individual channels 15 a to 15 c in which the second electrodes 22 a, 22 b, and 22 c are formed, up to the lower surface of the channel forming member 31 are formed by a method such as the laser machining, and an electroconductive material 28 is filled