A streamlined flat windscreen wiper for a vehicle is disclosed. The flat wiper includes a longitudinal wiper blade, at least one longitudinal stiffening member, a longitudinal member for retaining the wiper blade and the stiffening member, a longitudinal streamlined portion comprising two terminal caps and a central mounting extending between the terminal caps and being connected thereto. The mounting includes means for fixing to the stiffening member or to the member for retaining the stiffening member, and each cap includes means for guiding in translation terminal parts of the member.