PURPOSE: To reduce the production cost by decreasing the number of parts of a catadioptric system used for binoculars, etc., and facilitating assembling and adjusting work.

CONSTITUTION: Optical members 2 and 3 are arranged to be opposed to each other on an optical axis 1, and constitute the objective lens of the binoculars. Reflection layers 21 and 31 are formed at the parts of transparent bodies 20 and 30 in the optical members 2 and 3. Lens parts 23 and 33 and reflection parts 24 and 34 are formed to be planar and semicircular on the transparent bodies 20 and 30, and the lens parts 23 and 33 are opposed in reverse attitude so as to be opposed to the reflection parts 24 and 34. Light transmitted through the lens part 23 passes the reflection parts 34 and 24 and the lens part 33, and reaches an eye point through an ocular 4.