An fθ lens includes first and second lens groups arranged in this order from the entrance pupil side. The first lens group consists of a first lens having a negative or positive refracting power. The second lens group consists of a second lens having a positive refracting power and a third lens having a negative refracting power with the second and third lenses being cemented together. The second lens group has a positive refracting power as a whole. The following formulae (1) to (4) are satisfied. (1) 12≦ν d2 -ν d3 (2) -0.035≦Σ(φ i /ν di )≦0.005 (3) 0.7≦φ 23 ≦2.0 (4) 0.03≦d 12 ≦0.20 wherein φ i represents the power of i-th lens as numbered from the entrance pupil side standardized on the basis of the power of the whole system, φ 23 represents the power of the second lens group standardized on the basis of the power of the whole system, ν di represents the Abbe's number for the sodium d-line of i-th lens as numbered from the entrance pupil side and d 12 represents the surface separation between the first and second lens groups standardized on the basis of the focal length of the whole system.