A turbofan having a fixed structure, a fan, a fan casing surrounding the fan, an outer cowl disposed around the fan casing and mounted so as to be articulated on the fixed structure, and a deployment system that moves the outer cowl from a closed position to an open position. The deployment system has a guide rail fastened around the fan casing, a slider that is able to move along the guide rail and has a shoe. An activation system of the deployment system moves the slider and the shoe alternately in one direction or the other along the guide rail. One end of an arm of the deployment system is mounted to be articulated on the shoe and another end is mounted to be articulated on the outer cowl. Such a motorized deployment system makes it possible to save space and mass in the turbofan.