An f-θ lens (230) is joined to a mount through a light curable bond (141), forms an incident deflected beam onto a photosensitive body (245), and includes a lens part (110) which has an incident side (110a) on which the deflected beam is incident, and an exiting side (110b) which is disposed near the photosensitive body (245) and on which the entered deflected beam is exited, an joining part (120) which has a joining side (120a) which is extended from the incident face and is joined to the mount, and an emitting side (120b) which is extended from the exiting face and disposed to face the joining side (120a), and which a light beam for curing the light curable bond (141) is scanned, and an emitting part (130) which is formed on the emitting side (120b) in a nonplanar shape and provided to decrease loss of light quantity of the light beam scanned on the emitting face, so that the f-θ lens (230) provides an improved joining force in a joining process by a light cure joining type.