The object of this invention is to provide a phase stabilization device for stimulated brillouin scattering-phase conjugate mirrors and a light amplification apparatus using the phase stabilization device. A light amplification apparatus of the present invention includes a polarizer (70) for polarizing light beams reflected from a plurality of stimulated brillouin scattering-phase conjugate mirrors and causing the light beams to interfere with each other. A detector (80) acquires an interfering beam resulting from interference of the polarizer (70), and outputs the interfering beam. A phase controller (90) controls phase using the interfering beam acquired by the detector. Therefore, the apparatus of the present invention can stably lock the phase for a long period of time, and can be used in various industries and for scientific research in cases where a high repetition rate and high power are required.