An optical scanning apparatus and an image forming apparatus are provided; the optical scanning apparatus includes a light source, a deflecting unit, a reflection mirror, a casing, and first and second leaf springs. The casing includes first and second mirror supporting portions and a facing portion. The following relationship is satisfied: D2 < L + W - D1. With respect to a longitudinal direction, L is a length of the reflection mirror, D1 is a longest distance between the first and second supporting portions, W is a contact width of the second supporting portion to the reflection mirror, andD2 is a distance between the facing portion and a closest position thereto of the first supporting portion. The first and second leaf springs urge the reflection mirror against the first and second mirror supporting portions, respectively. At least one of the first and second leaf springs is bonded to the reflection mirror with an adhesive.