A laser beam scanning apparatus having a laser beam generating section generating first and second laser beams, a rotatable polygonal mirror for deflecting the first and second laser beams to form scanning lines each extending in a main scanning direction on a beam receiving surface and an optical system for imaging the first and second laser beams deflected by the polygonal mirror on the beam receiving surface. Each of the first and second laser beams impinges on the reflective face of the polygonal mirror at an angle with respect to an optical axis in a sub-scanning direction perpendicular to the main scanning direction. The following condition is satisfied:.vertline..beta..times.tan.theta.a.vertline..ltoreq.(5/3).times.Pi.vertline..beta..times.tan.theta.b.vertline..ltoreq.(5/3).times.Pi.vertline..theta.a.vertline.+.vertline..theta.b.vertline..gtoreq..vertline..psi.a.vertline.+.vertline..psi.b.vertline.where .beta. is a magnification of the optical system in the sub-scanning direction, .theta.a and .theta.b are angles at which the first and second laser beams impinge on the reflective face in the sub-scanning direction, respectively, Pi is a pitch of the scanning lines on the beam receiving surface in the sub-scanning direction, .psi.a and .psi.b are converging angles of the first and second laser beams impinging on the reflective face in the sub-scanning direction, respectively.