Provided are a telephoto zoom lens system and an electronic apparatus including the telephoto zoom lens system. The telephoto zoom lens system includes a first lens group having a positive refractive power and is fixed when zooming and focusing, a second lens group having a negative refractive power, a third lens group having a negative refractive power and performs focusing, a fourth lens group having a positive refractive power, and a rear lens group comprising one or more lens groups located between the fourth lens group and an image side. At least one lens group of the rear lens group is fixed while zooming, and a focal length thereof is unchanged while zooming.