Patent ID: 7068410

Claim:
An optical scanning apparatus which makes a light beam scan on a surface-to-be-scanned in a main scanning direction, comprising: a deflector in which a movable member, which includes a deflection mirror surface which is shaped like an elongated strip which elongates in said main scanning direction, is integrated with a support member which supports said movable member in such a manner that said movable member can freely pivot about a pivot axis which is approximately orthogonal to said main scanning direction, said deflector driving said movable member to pivot about said pivot axis, thereby deflecting said light beam which is incident upon said deflection mirror surface; a light source emitting said light beam; a first optical system which shapes said light beam from said light source into an elongated cross sectional shape which elongates in said main scanning direction, and makes said light beam impinge upon said deflection mirror surface from a front side to said deflection mirror surface along a direction of said pivot axis at an acute angle with respect to a surface normal to said deflection mirror surface; and a second optical system which images said light beam deflected by said deflection mirror surface on said surface-to-be-scanned, wherein said movable member is formed so that a width Hb of said movable member in the direction of said pivot axis satisfies a relationship: Mb+ 1.5 Ds<Hb<Mb+ 1.5 Ds+ 2 t, where Mb is a maximum displacement of said light beam on said deflection mirror surface in the direction of said pivot axis, Ds is a beam diameter on said deflection mirror surface in the direction of said pivot axis, and t is a thickness of said movable member, and wherein said movable member is formed so that a length Ha of the movable member satisfies a relationship: Ha≧ 1.5 Dm, where Dm is the beam diameter on said deflection mirror surface in a main scanning direction.