A thin plate stacked structure is formed of 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. The stacked structure further includes a release groove, an air release hole and an opening that is formed on the thin plate disposed at an 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.