  We propose a simple method by which we can explain the magnetic-field
dependence of the longitudinal ultrasonic attenuation in a type-II
superconductor. It gives a curve which is in good agreement with experimental
data, in paticular, near the lower critical field H_c1. We compare it with
conventional methods, which is not in good agreement with the experimental data
near H_c1 but near the upper critical field H_c2.
