Brillouin scattering method is a nondestructive and noncontact technique to measure local longitudinal and shear acoustic velocities in the GHz range. However, the measurements of weak scattering from thermal phonons result in the lower measurement accuracy and longer measurement time. To overcome this problem, a technique with artificially induced acoustic phonons was developed using a polycrystalline ZnO film, with a coaxial resonator to apply electric field. In this study, we observed Brillouin scattering by induced longitudinal phonons from ZnO film deposited on the rear surface of a plate sample. We investigated the relationship between the intensity of induced acoustic phonons and the input microwave power of a coaxial resonator. The effect of incident angle of light was also investigated.