Abstract: The purpose of the present invention is to improve, by providing, in the terminals of thermoelectric materials and electrodes or the inside of the material, one or more spaces or either thin or fine line structures in spaces such that heat transfer or working substance (WS) flow is prevented from propagating, figure-of-merit of thermoelectric materials without the same. Thermal conductivity due to causes other than WS that can move within a thermoelectric conversion element can be reduced by providing the spaces, alternatively, microstructures in thermoelectric materials. If the terminal of thermoelectric material or surfaces facing the terminal of the thermoelectric material is modified and/or the steeple tips or steeples formed on the terminal, the potential barrier height for WS can be reduced or the tunnel potential barrier width can be reduced when WS leaps into the space from the surface of the steeple tips or the steeples.