An optical device that allows laser beams to be incident to one end of an image fiber and receives a two-dimensional image of a laser irradiation target transmitted through the image fiber. The optical device includes: a mirror that is arranged on the one end side of the image fiber, reflects the laser beams, and transmits the two-dimensional image a laser beam source that allows the laser beams to be incident to the one end of the image fiber through reflection of the mirror an imaging device that receives the two-dimensional image from the one end of the image fiber through transmission of the mirror and an incidence control device that allows the laser beams to be incident to some cores out of the plurality of cores in the one end of the image fiber and changes cores to which the laser beams are incident.
