Intermediate lens barrel for microscope

An intermediate lens barrel for a microscope, in which an image is formed only once, the direction of the image does not change when returning to the original optical path, and no pupil aberration occurs. In this intermediate lens barrel, assuming that its round optical path is formed by n pieces of reflecting surfaces R (n being an even number not smaller than 4), an intermediate image is formed once in the round optical path, the angle formed by the normal N1 of the first reflecting surface R1 and the normal N2 of the second reflecting surface R2 with respect to each other when projected onto a plane orthogonal to the optical axis X1 reflected by the first reflecting surface R1 is alpha 1, the angle formed by the normal NN of the reflecting surface RN and the normal N1 of the reflecting surface R1 with respect to each other when projected onto a plane orthogonal to the optical axis XN reflected by the reflecting surface RN is alpha N, the relationship: ( alpha 1+ alpha 3+ . . . + alpha N-1)-( alpha 2+ alpha 4+ . . . + alpha N)=180 DEG ++360 DEG xn (n being an integer) is satisfied.