The optical scanning device scans an object with plural laser beams, and includes a light source, which emits plural parallel laser beams in a predetermined direction and which has a stem portion having a first notch; and a support having an opening, with which the light source is engaged so as to be rotatable on an axis parallel to the plural light beams, and a second notch located on a part of the opening so as to overlap with the first notch when the light source is engaged with the opening. By inserting a slotted screwdriver, etc., into the space formed by the two notches and rotating the screwdriver, the angle of the light source can be adjusted and thereby the pitches of the laser beams can be adjusted.