To easily cope with a change in the image pickup size, etc., of a video camera to be used by disposing a front group consisting of a convex lens group and a rear group consisting of a convex lens group in this order from a specimen side and making the rear group interchangeable independently.

This relay lens is equipped with a front group lens 11 and a rear group lens 12 in order from a specimen 2 side and an optical path changing prism 13 is disposed on an optical axis X between the both convex lens groups 11 and 12. The lens 11 is disposed to be movable in the optical axis direction. Namely, the deviation of an image-formation position is corrected by moving the lens 11 in the optical axis direction. Further, the lens 12 is made interchangeable. Therefore, by interchanging the lens 12, the focal distance of a relay lens system is changed. Thus, the focal distance is changed by interchanging only a part of the relay lens.