A linear imaging lens element for a scanning optical system in which light flux from a light source is formed as a linear image in the vicinity of a reflection surface of a light deflector includes a progressive power toric-aspherical surface being provided on either a surface facing the light source or on a surface facing the deflector. Cross-sectional configurations of the progressive power toric-aspherical surface, which are parallel with the plane including the optical axis and being perpendicular to the linear image, are made to be a circular arc, and the radius of curvature of each circular arc cross-sectional configuration is independently determined from the cross-sectional configuration lain on the plane which includes the optical axis and is parallel with the linear image.