An assembly comprising: an immersion lens supporting device; and an immersion lens movably supported by the immersion lens supporting device in a direction perpendicular to an optical axis (Ax) of an objective lens between the objective lens and a sample of an observation object, wherein the immersion lens supporting device comprises: a lens holder holding the immersion lens in a free state in which a lens bottom surface protrudes downward through a lower opening so as not to fix the immersion lens, characterized in that the immersion lens supporting device further comprises: a lens cover which is provided to an upper opening of the lens holder, and in which a cover bottom surface on the immersion lens side is on a plane perpendicular to the optical axis, the lens cover being configured to come into one-point contact with a spherical lens top surface of the immersion lens when the lens holder is further lowered after the immersion lens has come into contact with the surface of the sample, wherein the lens cover is provided with a positioning portion having a predetermined pattern which is capable of functioning as a visual reference for positioning of the immersion lens with respect to the objective lens, with reference to an image of the lens cover observed via the objective lens. an immersion lens supporting device; and an immersion lens movably supported by the immersion lens supporting device in a direction perpendicular to an optical axis (Ax) of an objective lens between the objective lens and a sample of an observation object, wherein the immersion lens supporting device comprises: a lens holder holding the immersion lens in a free state in which a lens bottom surface protrudes downward through a lower opening so as not to fix the immersion lens, characterized in that the immersion lens supporting device further comprises: a lens cover which is provided to an upper opening of the lens holder, and in which a cover bottom surface on the immersion lens side is on a plane perpendicular to the optical axis, the lens cover being configured to come into one-point contact with a spherical lens top surface of the immersion lens when the lens holder is further lowered after the immersion lens has come into contact with the surface of the sample, wherein the lens cover is provided with a positioning portion having a predetermined pattern which is capable of functioning as a visual reference for positioning of the immersion lens with respect to the objective lens, with reference to an image of the lens cover observed via the objective lens. a lens holder holding the immersion lens in a free state in which a lens bottom surface protrudes downward through a lower opening so as not to fix the immersion lens, characterized in that the immersion lens supporting device further comprises: a lens cover which is provided to an upper opening of the lens holder, and in which a cover bottom surface on the immersion lens side is on a plane perpendicular to the optical axis, the lens cover being configured to come into one-point contact with a spherical lens top surface of the immersion lens when the lens holder is further lowered after the immersion lens has come into contact with the surface of the sample, wherein the lens cover is provided with a positioning portion having a predetermined pattern which is capable of functioning as a visual reference for positioning of the immersion lens with respect to the objective lens, with reference to an image of the lens cover observed via the objective lens. a lens cover which is provided to an upper opening of the lens holder, and in which a cover bottom surface on the immersion lens side is on a plane perpendicular to the optical axis, the lens cover being configured to come into one-point contact with a spherical lens top surface of the immersion lens when the lens holder is further lowered after the immersion lens has come into contact with the surface of the sample, wherein the lens cover is provided with a positioning portion having a predetermined pattern which is capable of functioning as a visual reference for positioning of the immersion lens with respect to the objective lens, with reference to an image of the lens cover observed via the objective lens.