A thermoelectric material element includes: a thermoelectric material portion composed of a thermoelectric material that includes a first crystal phase and a second crystal phase during an operation, the second crystal phase being different from the first crystal phase; a first electrode disposed in contact with the thermoelectric material portion; and a second electrode disposed in contact with the thermoelectric material portion and disposed to be separated from the first electrode. During the operation, the thermoelectric material portion includes a first temperature region having a first temperature, and a second temperature region having a second temperature lower than the first temperature of the first temperature region. A ratio of the first crystal phase to the second crystal phase in the first temperature region is larger than a ratio of the first crystal phase to the second crystal phase in the second temperature region.