PROBLEM TO BE SOLVED: To provide a whole circumference observation optical system capable of acquiring high resolution without increasing a diameter of a tip portion and simultaneously distorting observation target images over the whole side circumference and to provide a whole circumference observation system including the whole circumference observation optical system.SOLUTION: The whole circumference observation optical system includes: three or more reflection surfaces 1a respectively forming pyramid surfaces symmetrical about an axis O, respectively arranged in the vicinities of a side observing first pupil position P1 respectively symmetrical about the axis O to divide beams from an observation target over the whole side circumference into beams in each of three or more side areas and reflect the divided beams backward a relay optical system 2 arranged on the axis O to enlarge and relay a pupil on the pupil position P1 to a side observing second pupil position P2 which are respectively symmetrical about the axis O three or more side observing aperture stops 3a arranged on pupil positions conjugate with the pupil position P1 three groups or more side observing image forming optical systems 3b arranged correspondingly to the aperture stops 3a and three or more side observing imaging elements 3c arranged correspondingly to the image forming optical systems 3b.
