A high gain solid-state laser apparatus capable of generating short-pulse terahertz waves with high efficiency is provided. The apparatus includes laser gain media 1 and an optical switch 3 that entraps seed light from a laser oscillator into the apparatus and outputs amplified laser light pulses from the apparatus. In the apparatus, ytterbium-doped lutetium lithium tetrafluoride (LuLiF4) crystal that is cooled below the liquid-nitrogen temperature is used as the laser gain media.