A thermoelectric conversion element (1, 101, 201, 301) comprising: a substrate including a first main face and a second main face located on the opposite side of the first main face; a first electrode provided on the first main face, an n-type thermoelectric conversion layer electrically connected to the first electrode, a p-type thermoelectric conversion layer in contact with the n-type thermoelectric conversion layer, and a second electrode electrically connected to the p-type thermoelectric conversion layer; a sealing layer provided on the first main face, the sealing layer covering the first electrode, the n-type thermoelectric conversion layer, the p-type thermoelectric conversion layer, and the second electrode; and a first high thermal conduction portion, a second high thermal conduction portion, and a low thermal conduction portion provided only on the second main face, wherein the first electrode, the n-type thermoelectric conversion layer, the p-type thermoelectric conversion layer, and the second electrode are arranged in order along an alignment direction orthogonal to a thickness direction of the substrate, wherein the first electrode is overlapped with the first high thermal conduction portion in the thickness direction, the second electrode is overlapped with the second high thermal conduction portion in the thickness direction, and a contact portion between the n-type thermoelectric conversion layer and the p-type thermoelectric conversion layer is overlapped with the low thermal conduction portion in the thickness direction, and wherein the sealing layer constitutes an outermost layer located on the first main face. a substrate including a first main face and a second main face located on the opposite side of the first main face; a first electrode provided on the first main face, an n-type thermoelectric conversion layer electrically connected to the first electrode, a p-type thermoelectric conversion layer in contact with the n-type thermoelectric conversion layer, and a second electrode electrically connected to the p-type thermoelectric conversion layer; a sealing layer provided on the first main face, the sealing layer covering the first electrode, the n-type thermoelectric conversion layer, the p-type thermoelectric conversion layer, and the second electrode; and a first high thermal conduction portion, a second high thermal conduction portion, and a low thermal conduction portion provided only on the second main face, wherein the first electrode, the n-type thermoelectric conversion layer, the p-type thermoelectric conversion layer, and the second electrode are arranged in order along an alignment direction orthogonal to a thickness direction of the substrate, wherein the first electrode is overlapped with the first high thermal conduction portion in the thickness direction, the second electrode is overlapped with the second high thermal conduction portion in the thickness direction, and a contact portion between the n-type thermoelectric conversion layer and the p-type thermoelectric conversion layer is overlapped with the low thermal conduction portion in the thickness direction, and wherein the sealing layer constitutes an outermost layer located on the first main face.