A wind turbine blade (10) for a rotor of a wind turbine (2) having a substantially horizontal rotor shaft, said rotor comprising a hub (8), from which the blade (10) extends substantially in a radial direction when mounted to the hub (8), the blade having a longitudinal direction (r) with a tip end (14) and a root end (16) and a transverse direction, is disclosed. The blade further comprises: a profiled contour (40, 42, 50) including a pressure side and a suction side, as well as a leading edge (18) and a trailing edge (20) with a chord having a chord length extending there between, the profiled contour, when being impacted by an incident airflow, generating a lift. The wind turbine blade is provided with a longitudinally extending flow guiding device (70, 170) attached to the profiled contour. The flow guiding device comprises: a base (90, 190) having a first longitudinal end (91, 191) nearest the root end (16) and a second longitudinal end (92, 192) nearest the tip end (14), a first side (93, 193) nearest the leading edge (18) and a second side (94, 194) nearest the trailing edge (20), as well as a first surface (95, 195) and a second surface (96, 196), the first surface of the base being attached to the profiled contour, and the second surface facing away from the profiled contour. A longitudinally extending substantially plate-shaped element (97, 197) protrudes from the second surface (96, 196) of the base (90, 190).