In the optical beams scanning apparatus and an image forming apparatus having this optical beam scanning apparatus according to this invention, a light emitting unit emits plural laser beams set at a predetermined output in advance, and a scanning unit deflects the emitted plural laser beams and scans with them. A laser beam output setting unit arranges the light emitting unit so that scanning positions of the plural laser beams are arrayed in time series in a main scanning direction on the same line, and sets the output of laser beams cast onto a photoconductor by using the plural laser beams. A writing unit writes an image to the photoconductor with the preset output of the laser beams cast onto the photoconductor, using the plural laser beams used for scanning. With the optical beam scanning apparatus and the image forming apparatus having this optical beam scanning apparatus according to this invention, the output of laser beams cast onto a photoconductive drum can be controlled at a high speed.