Provided is a collision avoidance apparatus that can avoid a collision through both steering and braking. In a collision avoidance apparatus, a no-entry zone defining unit defines a no-entry zone for preventing a subject vehicle from colliding with an obstacle around the subject vehicle, based on obstacle information including information on a position of the obstacle and based on lane information that is information on a traveling lane of the subject vehicle. A following determination unit determines whether the obstacle is an avoidance target or a following target, based on the position of the obstacle or a position of the no-entry zone. A constraint establishing unit establishes a constraint on a state quantity or a control input of the subject vehicle to prevent the subject vehicle from at least entering the no-entry zone.