To provide a holding structure of laser oscillator in which a laser oscillator held on a base can secure a specified optical path appropriately even if a vibration acts on the laser oscillator at the time of transportation due to heating of the laser oscillator or thermal deformation of the base caused by outer temperature.

The holding structure comprises a first holding means 26 for holding one end part in the optical path direction of a holder 10 freely movably in the tree-dimensional direction about a specified point with respect to a base 8, and second and third holding means 33 and 34 for holding the other end part in the optical path direction opposing the one end part of the holder 10 with respect to the base 8 such that it has a specified degree of freedom in all free directions on the same plane parallel with the base 8.