The Doppler effect is discussed for flexure waves in a beam and a plate, three body waves (P, SV, SH) in an infinite solid, modal SH waves in a thick plate and Rayleigh wave on the surface of a semi-infinite solid. The exact closed form solution for each elasto-dynamic problem is obtained and the simple equation for the Doppler frequency shift is derived for all waves. It is shown that the Doppler frequency shift takes place continuously in the 2D plane problems, and that the most sensible wave for the Doppler frequency shift is the non-dispersion wave, such as the body wave and Rayleigh wave. The flexure and modal waves, which have the dispersion nature, is less sensible.