The description relates to a loading trailer which comprises a wheel bogie (4), a chassis (2) supported by the wheel bogie, and a gooseneck (3) for connection to a drive vehicle. The chassis is lowerable and raisable in relation to the wheel bogie for the purpose of being driven under a flat bed (5) and for lifting the flat bed with its load. In order to facilitate the aligning of the loading trailer (1) when driving it under the flat bed, at least the rear part of the chassis (2) is equipped with aligning guides (6) which work against the inner sides of the flat bed (5). The aligning guides (6) are preferably made up of arms which extend obliquely forwards and are adjustable by hydraulic cylinders and which have at their ends guide rolls which in the final position can be locked in depressions (9) in the flat bed. The front part of the chassis (2) also has preferably guides (7), which may be fixed.