We report on the four-pass amplifier which has operational reliability for dumping an amplified pulse and produces no hot spot which usually causes optically induced damage in the gain medium. By compensating for the polarization distortion caused by thermal birefringence, we could obtain the gain of 2.5 x 10(5) from the amplifier. Without compensating for the polarization distortion, we could not obtain the gain larger than 6 x 10(3) because of lasing and generation of a large number of pulses.