Mower including a suspension device connecting a harvesting mechanism to a chassis and allowing the harvesting mechanism a heightwise movement with respect to the chassis. The mower further including a lightening device associated with the harvesting mechanism and including two elastically deformable members extending transversely to a direction of forward travel during work, each elastically deformable member acting, via a first of its ends, on a corresponding end of the harvesting mechanism. The mower including a centralized device for adjusting the lightening force exerted on the harvesting mechanism, where the device is coupled to the second ends of the elastically deformable members. The centralized device for adjusting the lightening force exerted on the harvesting mechanism includes a rotary control member connected to the chassis and coupled to each second end of the elastically deformable members via a configuration which converts the rotation of the rotary control member into an action of stressing or relaxing the elastically deformable members depending on the direction in which the rotary control member is turned.