A detailed investigation is given of the ultrasonic attenuation governed by dynamical properties of conduction electrons. It is pointed out that the ultrasonic attenuation arises from the same mechanism that is also responsible for the attenuation of collective oscillations in a conduction electron system, known as Landau's attenuation in some case. Applying the electro-magnetic dispersion relations in metals to the problem in hand, the attenuation constants are derived, and at the same time, the effects of conduction electrons on sound velocities are investigated. Some discussions are given of the relation between the results obtained and those of Pippard. Then the parallelism of the present phenomenon with the anomalous skin effect is pointed out and the attenuation constants are derived for the case where the energy of a conduction electron is an arbitrary function of the wave vector. As a by-product, the most general expression for Landau's dismagnetic susceptibility is derived with some applications.