A light scanning unit and an electrophotographic image forming apparatus are provided. The light scanning unit includes a light source unit for emitting a light beam, a light deflector for scanning and deflecting the light beam, an imaging optical system having an imaging lens for imaging the scanned and deflected light beam, and first and second reflection members arranged on an optical path, a housing, and first and second assembly members for pressing and fixing the first and second reflection members on the housing. The assembly members press and fix the reflection members on the housing by pressing the reflection members in a direction in which curvature of a scanning line due to the inclination of the first reflection member and curvature of a scanning line due to the inclination of the second reflection member are offset with each other.