A stacked structure is formed such that a plurality of thin plates, which include at least one liquid flow passage thin plate provided with a liquid flow passage having a predetermined pattern formed on at least one surface, are stacked with an adhesive. A release groove for releasing the adhesive is formed on the liquid flow passage thin plate. An air release hole, which is communicated with the release groove and which penetrates in the stacking direction, is bored through a thin plate stack stacked on the liquid flow passage thin plate. An opening, which allows the air release hole to be open to the outside, is formed on the thin plate disposed at the outermost layer of the thin plate stack. The air release hole has a diameter which is larger than the width of the release groove and which is larger than the opening disposed on the outermost layer. Any excessive adhesive is accumulated in the air release hole, and it is possible to greatly decrease the amount of the adhesive outflowing to the outside of a cavity unit.