Agricultural device for processing crop which lies loosely on the ground, for example mowed grass, which agricultural device comprises a trailer which can be coupled to a tractor, which trailer is provided with: - an undercarriage having a central longitudinal axis, which undercarriage is provided with: • a coupling member for coupling to a tractor, • a plurality of wheels by means of which the undercarriage can travel on the ground, - a crop-processing device which is provided with: • a tilting frame which is connected to the undercarriage so as to be tiltable about a tilting axis which runs substantially transversely with respect to the longitudinal axis of the undercarriage, • two supporting arms (20, 21) which extend on either side of the tilting frame, which supporting arms (20, 21) are each connected to the tilting frame so as to be pivotable about a swivel axis (22, 23) which runs substantially transversely with respect to the tilting axis, and which supporting arms (20, 21) each comprise a plurality of supporting arm portions (24, 24A) which are connected to each other so as to be hingable about hinge axes which run substantially parallel to the swivel axis (22, 23) of said supporting arm (20, 21), • crop-processing members which are fitted to the supporting arm portions (24, 24A) of the supporting arms (20, 21) so as to be rotatable, wherein the crop-processing device is movable from a transport position to an operating position, wherein, in the transport position, the tilting frame has a raised position in which the swivel axes (22, 23) of the supporting arms (20, 21) run substantially vertically, and each supporting arm (20, 21) has a collapsed position, in which said supporting arm (20, 21) runs substantially parallel to the longitudinal axis of the undercarriage, and when moving the crop-processing device from the transport position to the operating position, each supporting arm (20, 21) is swung outwards about the swivel axis (22, 23) thereof, from the collapsed position into an extended position, in which said supporting arm (20, 21) extends outwards substantially transversely with respect to the longitudinal axis of the undercarriage, and subsequently the tilting frame is tilted downwards about the tilting axis, from the raised position to a lowered position, in which the crop-processing members are oriented for processing crop which is lying loosely on the ground, in which case the operating position has been reached, characterized in that each supporting arm (20, 21) is provided with at least one actuating member which is arranged between two adjacent supporting arm portions (24, 24A) of said supporting arm (20, 21) which are hingably connected to each other and the actuating members are configured to bring and/or keep said supporting arm portions (24, 24A) of each supporting arm (20, 21) substantially in line with each other while the supporting arms (20, 21) are being swung outwards from the collapsed position to the extended position, in such a manner that the centre of gravity of the crop-processing device, in the extended position of the supporting arms (20, 21), viewed in the direction of the longitudinal axis of the undercarriage, is situated behind the tilting axis and the crop-processing device descends into the operating position on account of its own weight. - an undercarriage having a central longitudinal axis, which undercarriage is provided with: • a coupling member for coupling to a tractor, • a plurality of wheels by means of which the undercarriage can travel on the ground, • a coupling member for coupling to a tractor, • a plurality of wheels by means of which the undercarriage can travel on the ground, - a crop-processing device which is provided with: • a tilting frame which is connected to the undercarriage so as to be tiltable about a tilting axis which runs substantially transversely with respect to the longitudinal axis of the undercarriage, • two supporting arms (20, 21) which extend on either side of the tilting frame, which supporting arms (20, 21) are each connected to the tilting frame so as to be pivotable about a swivel axis (22, 23) which runs substantially transversely with respect to the tilting axis, and which supporting arms (20, 21) each comprise a plurality of supporting arm portions (24, 24A) which are connected to each other so as to be hingable about hinge axes which run substantially parallel to the swivel axis (22, 23) of said supporting arm (20, 21), • crop-processing members which are fitted to the supporting arm portions (24, 24A) of the supporting arms (20, 21) so as to be rotatable, • a tilting frame which is connected to the undercarriage so as to be tiltable about a tilting axis which runs substantially transversely with respect to the longitudinal axis of the undercarriage, • two supporting arms (20, 21) which extend on either side of the tilting frame, which supporting arms (20, 21) are each connected to the tilting frame so as to be pivotable about a swivel axis (22, 23) which runs substantially transversely with respect to the tilting axis, and which supporting arms (20, 21) each comprise a plurality of supporting arm portions (24, 24A) which are connected to each other so as to be hingable about hinge axes which run substantially parallel to the swivel axis (22, 23) of said supporting arm (20, 21), • crop-processing members which are fitted to the supporting arm portions (24, 24A) of the supporting arms (20, 21) so as to be rotatable,