To provide a diffraction optical element in which mold release resistance at injection molding of a resin-made diffraction optical element having a diffraction face is reduced, the light transmission quantity at the diffraction face is reduced, and reflection light is restrained from becoming ghost light, and to provide an optical scanner and an image forming apparatus.

The diffraction optical element has stepped parts of which the cross section has a stepped pattern and a plurality of flat face parts which are adjacent to the stepped part and generate power. The diffraction optical element has a fine pattern on the stepped part. Thus, the light transmission quantity at the diffraction face is reduced and the reflection light is restrained from becoming the ghost light.