The wall of each supply path formed in a silicon substrate has such a shape that a plurality of regions distinguished from each other due to different inclinations to a first surface of the silicon substrate are connected to each other between the first surface and a second surface of the silicon substrate and the width of the supply path is maintained or expands from the first surface to second surface of the silicon substrate. An internal opening is formed by one of the regions that is most steeply inclined to the first surface of the silicon substrate. A region reducing the squeezing of an adhesive into the internal opening is placed between the internal opening and the second surface of the silicon substrate.