To take out energy as electric energy while eliminating energy consumption by dispensing with energy input from the outside in cooling a system surrounded by a heat insulating material.

Electromagnetic wave generated by black body radiation by material existing inside a system to be cooled is converted into electric energy using a device 2 generating power using electromagnetic wave. The electric energy is carried to the outside of the system through a conductor 3. Energy inside the system is thereby reduced to attain a drop of temperature. Further, energy is not consumed in cooling the system but can be taken out as electric energy to the outside.