Appropriate amount of brazing material is put on each of inner and outer recessed portions of a first heat storing element. Then, the first heat storing element is placed close to and substantially parallel to a second heat storing element, and an inner projected portion of the second heat storing element is fitted into the inner recessed portion of the first heat storing element, and simultaneously an outer projected portion of the second heat storing element is fitted into the outer recessed portion of the first heat storing element.