Abstract: A container for a liquid reaction mixture whereby the liquid reaction mixture is brought into contact with a heater at a specified temperature and thus a nucleic amplification reaction is promoted, which has a substrate having a front surface and a back surface and being constructed so that either or both of these surfaces are maintained in facing a heater and wells that are formed in the surface direction of the substrate separately and independently from each other and each holds the above-described liquid reaction mixture in a liquid-tight sealed state, characterized in that; the above-described wells each comprises an opening formed in the above-described substrate and blocking members whereby the front surface side and back surface side of the opening are blocked, and at least the blocking member that blocks the surface in the side being in contact with the above-described heater has a part made of a stretchable film having a thickness of 10 to 300 ?m.