The present invention relates to a laser apparatus with a structure for realizing a fast response in carrying out a start and an end of output of pulsed laser light while effectively suppressing damage to an optical amplifying medium. The laser apparatus is provided with a seed light source (10), an optical amplification section (20), a pulse modulator (40), a pump power controller (50), and a main controller (60). The pulse modulator receives an output start instruction and an output end instruction fed from the main controller and controls a start and an end of output of seed light from the seed light source. The pump power controller receives a pump trigger signal fed from the main controller and increases or decreases a power of pump light supplied to the amplification section. The main controller deceases the power of the pump light supplied to the amplification section, on the occasion of ending the output of the pulsed laser light, and thereafter makes the pulse modulator end the output of the seed light from the seed light source.