A multi-beam image forming apparatus includes: first and second semiconductor laser arrays each having n laser elements; a multi-beam generation unit that generates 2n laser beams by synthesizing laser beams generated by the first and second semiconductor laser arrays; a beam detection unit that generates synchronous detection signals to obtain synchronous scanning of the respective laser beams; and a control unit. The beam detection unit includes first and second beam detection units disposed substantially at a same position in a main scanning direction and adjacently disposed in a sub-scanning direction. The n laser beams of the first and second semiconductor laser arrays are detected by the first and second beam detection unit, respectively. The control unit controls image formation start positions of the 2n laser beams on the basis of the synchronous detection signals output from the first and the second beam detection units.