A diagonal strut device (1) for reinforcing arrangement on an undercarriage of a motor vehicle. A plurality of struts (2) made from a fiber-reinforced plastic composite material extend away from a central joint element (3). Each strut (2) can be connected to the undercarriage via this from the end facing away from the central joint element (3). For this, a connecting joint element (4) is arranged on the end of each strut (2) facing away from the central joint element (3), wherein the central joint element (3) and the connecting joint elements (4) are formed from a light metal material. The central joint element (3) and the connecting joint elements (4) are then connected to the struts (2) by an at least positive connection. The central joint element (3) and the connecting joint elements (4) are each formed from several individual elements joined together.