NOVELTY - The thermoelectric conversion material (8, 9) contains composition (1) comprising titanium, zirconium, hafnium, nickel and tin, and magnesium-silver-arsenic type crystal structure as main phase.    USE - For thermoelectric element (claimed) used in thermoelectric cell, and thermoelectric conversion module.    ADVANTAGE - The thermoelectric conversion material has high Seebeck coefficient, low resistivity and heat conductivity. Since a composition containing toxic elements is not used, the thermoelectric conversion material is manufactured safely and economically. The thermoelectric element and thermoelectric conversion module are produced easily.    DETAILED DESCRIPTION - The thermoelectric conversion material (8, 9) contains composition comprising titanium, zirconium, hafnium, nickel and tin, and magnesium-silver-arsenic type crystal structure as main phase. The composition is of formula (1): (Tia1Zrb1Hfc1)xNiySn100-x-y, where a1, b1 and c1 are between 0 and 1, and x and y are 30-35. Portion of zirconium, titanium or hafnium is substituted by tungsten, vanadium, niobium, tantalum, chromium or molybdenum. Portion of nickel is substituted by copper, manganese, iron, cobalt and portion of tin is substituted by arsenic, antimony, bismuth, germanium, lead, gallium or indium. Alternately, the composition is of formula (2): Ln1XNiYSb100-X-Y,    where Ln1 is scandium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, uranium or yttrium. Portion of Ln1 is substituted by titanium, zirconium, hafnium, lanthanum, cerium, promethium, neodymium, samarium, europium, beryllium, magnesium, calcium, strontium or barium.    Portion of nickel in the composition (2) is substituted by vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, cobalt, rhodium, iridium, palladium, platinum, gold, silver or zinc. Portion of antimony in the composition (2) is substituted by aluminum, silicon, gallium, germanium, arsenic, indium, tin, lead or bismuth.    An INDEPENDENT CLAIM is included for thermoelectric element.    DESCRIPTION OF DRAWING(S) - The figure shows the model of the thermoelectric element.    Thermoelectric conversion materials (8, 9)    Electrodes (10a, 10b)    Hole (14)    Electron (15)