A laser beam scanning optical apparatus which images each laser beam emitted from a laser diode array via a deflector and optical elements and scans the laser beam linearly on a scanning surface at a substantially constant speed. The laser diode array has a plurality of light emitting sources arranged two-dimensionally, and more specifically, arranged in a first direction at uniform intervals of P1 and in a second direction perpendicular to the first direction at uniform intervals of P2 which is different from P1. In the laser beam scanning optical apparatus, the magnification ratio in the main scanning direction and the magnification ratio in the sub scanning direction are different from each other. If there are a number m of light emitting sources in each line of the first direction at the intervals of P1 and a number n of light emitting sources in each line of the second direction at the intervals of P2, the first direction is at an angle &thgr; expressed by the following expression to the main scanning direction: &thgr;=tan−1(P2/mP1).