A focusing unit (11) is constituted of a prism base (11a), deflection prisms (11b and 11c), and a slit chart (11e) having a slit opening (11d), and the deflection prisms (11b and 11c) are arranged so that deflecting directions may become reverse. The slit opening (11d) is made equally to spread across the deflection prisms (11b and 11c) approximately and is impermeable except the slit opening (11d), and light incident on the deflection prisms (11b and 11c) passes only this slit opening (11d). In addition, the light which is emitted by a focus index illumination light source illuminates the slit opening (11d) through the deflection prisms (11b and 11c). As to an image of the illuminated slit opening (11d), two slit images are formed on a fundus of eye by actions of the deflection prisms 11b and 11c. Focus adjustment is made by aligning these slit images (S1 and S2) in a straight line.
