[Object] To increase the degree of freedom in designing a system for taking out power from a temperature gradient in terms of a thermoelectric conversion element or a thermoelectric conversion device.[Means for Achieving Object] A thermal spin-wave spin current generating member made of a magneto-dielectric body is provided with an inverse spin Hall effect member, a temperature gradient is provided in the above-described thermal spin-wave spin current generating member in the direction of the thickness, and at the same time a magnetic field is applied to the above-described inverse spin Hall effect member in the direction perpendicular to the longitudinal direction and perpendicular to the direction of the above-described temperature gradient by means of a magnetic field applying means so that a thermal spin-wave spin current is converted to a voltage which is taken out in the above-described inverse spin Hall effect member.