To obtain an optical scanning optical system constituted, so that changes in Fno in the main scanning direction is made small, and meeting the need for high image quality by making a spot diameter uniform, in spite of its compactness and a simple constitution, and to provide an imaging apparatus using the optical system.

This optical scanning optical system is provided with a 1st optical system for converting the state of luminous flux emitted from a light source to another state by a condenser lens, and a light deflector deflecting and making the changed luminous flux scan in the main scanning direction, and the luminous flux deflected to perform scanning by the light deflector is formed into an image in a spot state on the surface to be scanned and made to conduct scanning. The light deflector produces sinusoidal vibration, and the center axis of the sinusoidal vibration of the light deflector other than a deflect reflection surface exists and satisfies a conditional expression (2).