A thermoelectric conversion element, comprising: an n-type semiconductor; a p-type semiconductor; an n-side junction layer formed on each of a first surface and a second surface of the n-type semiconductor; a p-side junction layer formed on each of a first surface and a second surface of the p-type semiconductor; a first electrode which has one side joined to the first surface of the n-type semiconductor via the n-side junction layer, and the other side joined to the first surface of the p-type semiconductor via the p-side junction layer; and two second electrodes, one of which is joined to the second surface of the n-type semiconductor via the n-side junction layer and the other of which is joined to the second surface of the p-type semiconductor via the p-side junction layer, characterized in that: the n-type semiconductor has a composition represented by the following formula, the p-type semiconductor has a composition represented by the following formula, the first electrode and the second electrode include Ni as a main component, the n-side junction layer has an AlNi layer and an Al 3 Ni 2 layer in this order from the first electrode side or the second electrode side, and the p-side junction layer has a Ni 3 Sn 2 layer, an AlNi layer, and an Al 3 Ni 2 layer in this order from the first electrode side or the second electrode side, and the n-side junction layer and the p-side junction layer include Al: Mg 2 Si a Sn 1-a +A provided that, 0.25≤a≤0.75, and A includes at least one of Sb, Bi, and Fe Mg m Si x Sn y Ge z +B provided that, 1.98≤m≤2.01, 0≤x≤0.25, 0.60≤y≤0.95, z≥0, x+y+z=1, and -1.00x+0.40≥z≥-2.00x+0.10; if x is 0.00<x<0.25, -1.00y+1.00≥z≥-1.00y+0.75; if y is 0.60≥y≥0.90, -2.00y+1.90≥z≥-1.00y+0.75; if y is 0.90<y≤0.95, and B includes at least one of Group 1A alkali metals, Au, Ag, Cu, Zn, Ca, and Ga. an n-type semiconductor; a p-type semiconductor; an n-side junction layer formed on each of a first surface and a second surface of the n-type semiconductor; a p-side junction layer formed on each of a first surface and a second surface of the p-type semiconductor; a first electrode which has one side joined to the first surface of the n-type semiconductor via the n-side junction layer, and the other side joined to the first surface of the p-type semiconductor via the p-side junction layer; and two second electrodes, one of which is joined to the second surface of the n-type semiconductor via the n-side junction layer and the other of which is joined to the second surface of the p-type semiconductor via the p-side junction layer, characterized in that: the n-type semiconductor has a composition represented by the following formula, the p-type semiconductor has a composition represented by the following formula, the first electrode and the second electrode include Ni as a main component, the n-side junction layer has an AlNi layer and an Al 3 Ni 2 layer in this order from the first electrode side or the second electrode side, and the p-side junction layer has a Ni 3 Sn 2 layer, an AlNi layer, and an Al 3 Ni 2 layer in this order from the first electrode side or the second electrode side, and the n-side junction layer and the p-side junction layer include Al: Mg 2 Si a Sn 1-a +A provided that, 0.25≤a≤0.75, and A includes at least one of Sb, Bi, and Fe Mg m Si x Sn y Ge z +B provided that, 1.98≤m≤2.01, 0≤x≤0.25, 0.60≤y≤0.95, z≥0, x+y+z=1, and -1.00x+0.40≥z≥-2.00x+0.10; if x is 0.00<x<0.25, -1.00y+1.00≥z≥-1.00y+0.75; if y is 0.60≥y≥0.90, -2.00y+1.90≥z≥-1.00y+0.75; if y is 0.90<y≤0.95, and B includes at least one of Group 1A alkali metals, Au, Ag, Cu, Zn, Ca, and Ga. the n-type semiconductor has a composition represented by the following formula, the p-type semiconductor has a composition represented by the following formula, the first electrode and the second electrode include Ni as a main component, the n-side junction layer has an AlNi layer and an Al 3 Ni 2 layer in this order from the first electrode side or the second electrode side, and the p-side junction layer has a Ni 3 Sn 2 layer, an AlNi layer, and an Al 3 Ni 2 layer in this order from the first electrode side or the second electrode side, and the n-side junction layer and the p-side junction layer include Al: Mg 2 Si a Sn 1-a +A provided that, 0.25≤a≤0.75, and A includes at least one of Sb, Bi, and Fe Mg m Si x Sn y Ge z +B provided that, 1.98≤m≤2.01, 0≤x≤0.25, 0.60≤y≤0.95, z≥0, x+y+z=1, and -1.00x+0.40≥z≥-2.00x+0.10; if x is 0.00<x<0.25, -1.00y+1.00≥z≥-1.00y+0.75; if y is 0.60≥y≥0.90, -2.00y+1.90≥z≥-1.00y+0.75; if y is 0.90<y≤0.95, and B includes at least one of Group 1A alkali metals, Au, Ag, Cu, Zn, Ca, and Ga.