A layer structural complex magnetic refrigerant, which is suitable for the Ericsson cycle, satisfying the Carnot principle, has been investigated. Above ∼ 15 K, since the thermal agitation energy and the lattice entropy increase considerably, the ferromagnetic material has to be used for the refrigerant in the magnetic refrigeration. However, the variation of the magnetic entropy of the ferromagnets is not appropriate to the Ericsson cycle in which the entropy difference ΔS J between two kinds of the isomagnetic field processes should be constant in the refrigeration range. In order to make the refrigerant having constant ΔS J mentioned above, we made the layer structural sintered material composed of four kinds of ferromagnets, ErAl 2.2 , HoAl 2.2 , (Dy 0.5 Ho 0.5 )Al 2.2 and DyAl 2.2 , and investigated its entropy experimentally. As the result, it is verified that the layer structural magnetic material is one of the most promising refrigerant for the Ericsson cycle.