PURPOSE: To facilitate a laminating operation of heat storage elements and reduce the manufacturing cost of a heat accumulator by forming a heat storage elements of porous material and providing a space between the elements.

CONSTITUTION: A heat accumulator 2 of a regenerating heat exchanger to be used for an external combustion engine is formed of a plurality of heat storage elements 3 laminated coaxially in a casing 1. Each element 3 is formed in a shape having a disclike body 3a and a leg 3b protruding from one end face of the body 3a, and formed by integrally molding a porous material. The plurality of the elements 3 are so laminated as to generate a space 4 through the legs 3b in a flowing direction of operating gas to form the accumulator 2. Heat is transferred between the gas and the accumulator 2.