To provide an optical device and a monitor device for making it possible to obtain temporally high-resolution and smooth images which facilitate the detection of a lesion.

The optical device 2 comprises: light source parts 16A, 16B and 16C including a first light source for emitting a first laser beam and a second light source for emitting a second laser beam having a wavelength different from the first laser beam; an optical element 24 for irradiating an object with at least a part of the first laser beam as first illumination light and irradiating the object with at least a part of the second laser beam as second illumination light; an illumination light path part 22; an imaging part 36 for imaging a first image by receiving at least a part of the first illumination light and imaging a second image by receiving at least a part of the second illumination light reflected by the object; a reflected light path part 30; a control part 44 for controlling the changeover of the first illumination light and second illumination light and the changeover of the imaging of the first and second images synchronized with the changeover; and an image storage part 38 for preserving the first and second images imaged by the imaging part 36.