Abstract: A two-element f-? lens used for a micro-electro mechanical system (MEMS) laser scanning unit includes a first lens and a second lens, both in a meniscus shape having a concave surface facing the side of the MEMS reflecting mirror. The two-element f-? lens comprising a first lens with a first optical surface and a second optical surface and a second lens with a third optical surface and a fourth optical surface, both in a meniscus shape and having a concave surface on the side of the MEMS reflecting mirror; at least one optical surface is aspherical surface in both main scanning direction and sub scanning direction, and satisfies specifical optical conditions. The two-element f-? lens corrects the nonlinear relationship between scanned angle and the time into the linear relationship between the image spot distances and the time.