Optical unit and optical instrument having the same

An optical unit, comprising:

• an optical element for propagating incident light toward a predetermined direction;
• a barrel for supporting said optical element;
• and
• attenuating means including a plurality of grooved portions, for attenuating, through multiple reflection, at least a portion of light emitted from said optical element toward a direction different from the predetermined direction, wherein (i) said attenuating means includes two recesses each having a horn-like section shape, said two recesses being bent in directions away from each other, (ii) two of the grooved portions are provided on an inside wall of said barrel and at positions shifted in an optical axis direction of said optical element, (iii) one of the two grooved portions, which is provided at a light entrance side of said optical element, is bent toward a direction of incidence of the light, and (iv) the other of the two grooved portions, which is provided at a light exit side of said optical element, is bent toward a direction of emission of the light.