The temperature coefficient of Young’s modulus and rigidity modulus were determined with the alloys of 36%Ni, 10%Cr and the rest of iron, that is Elinvar, with added C from 0.16% to 0.5%. And it was found that an increase in C content of 0.1% resulted in a rise of temperature coefficients of those modulus of 1.3×10−5 and of 2.5×10−5 respectively; that is, the effect of the change of C content on those temperature coefficient was larger than in the case of change of Ni or Cr content. Considering that the chemical affinity of C atom to Cr atom is greater than to Fe or Ni atoms, it could be concluded that C atom combined with Cr atom, resulting in the change of the temperature coefficients.