The invention relates to a reaction vessel, a reaction vessel liquid introducing device, a liquid introducing and reaction measuring device, and a liquid introducing device, and is directed to being able to perform temperature control of a liquid stored within the reaction vessel with a high accuracy and faithful responsiveness. The reaction vessel comprises: a storage chamber in which a liquid is storable, that has an opening part; a reaction chamber that is formed thinner or narrower than the storage chamber; and at least one flow passage that communicates between the storage chamber or the exterior and the reaction chamber. The reaction vessel is formed such that it is connectable to a liquid introducing section provided externally, and the liquid can be introduced into the reaction chamber by connecting to the liquid introducing section.