To correctly arrange a centered target in the pupil surface of an objective or the aperture stop surface of a condenser lens by providing a holding means which holds the centered target on the pupil surface of the objective or the aperture stop surface of the condenser lens and has a size matching the focal length of the objective.

A target screen 10 is a disk, and a cross mark passing the center point of the disk and a concentric circle having its center at the intersection of the cross mark (the center of the disk) are drawn. The overall length of a cylindrical member 20 is nearly as large as the focal length of the objective and the member is formed of a transparent material. On the inner peripheral part of the cylindrical member 20, the target screen 10 is provided at the position where its top surface meets the pupil surface 10a when the cylindrical member 20 is set on the stage 101 of the microscope. Therefore, the cross mark and concentric circle on the target screen 10 positioned on The pupil surface 10a of the objective can be seen through the transparent part.