A focusing unit is constituted of a prism base, deflection prisms, and a slit chart having a slit opening, and the deflection prisms are arranged so that deflecting directions may become reverse. The slit opening is made equally to spread across the deflection prisms approximately and is impermeable except the slit opening, and light incident on the deflection prisms passes only this slit opening. In addition, the light which is emitted by a focus index illumination light source illuminates the slit opening through the deflection prisms. As to an image of the illuminated slit opening, two slit images are formed on a fundus of eye by actions of the deflection prisms. Focus adjustment is made by aligning these slit images in a straight line.
