A rigid endoscope system includes: a pipe body； an objective lens； an ocular lens； an image pick-up sensor； a light source that emits a detection light to an object to be observed； a light receiving sensor that receives the detection light reflected by the object to be observed and has passed through the inside of the pipe body； a spectroscopic device that spectrally disperses a luminous flux emitted from the ocular lens in each of a direction toward the image pick-up sensor and a direction toward the light receiving sensor； a unit that calculates a distance to the object to be observed； an image-forming system that forms an image of a portion of the luminous flux on the image pick-up sensor； and a focus adjustment unit that performs a focus adjustment by moving a lens included in the image-forming system in an optical axis direction based on the calculated distance.
