The emergence of the nematic order and fluctuations has been discussed as a central issue in Fe-based superconductors. To clarify the origin of the nematicity, we focus on the shear modulus C₆₆ and the Raman quadrupole susceptibility χ^Raman_x2−y2, Because of the Aslamazov-Larkin vertex correction, the nematic-type orbital fluctuations are induced, and they enhance both 1/C₆₆ and χ^Raman_x2−y2 strongly. However, χ^Raman_x2−y2 remains finite even at the structure transition temperature T_S, because of the absence of the band Jahn-Teller effect and the Pauli (intraband) contribution, as proved in terms of the linear response theory. The present study clarifies that the origin of the nematicity in Fe-based superconductors is the nematic orbital order and fluctuations.