This device comprises a sprayer (10) and a reservoir (9) for feeding the sprayer with fluid. The reservoir (9) defines a cylindrical housing (L9) in which there slides (F1) a piston (91) forming a moving wall (91a) for a storage volume (V9) for storing the coating fluid. The housing (L9) is defined by a jacket (92) placed in a support-forming body (95). The jacket (92) has an end wall (93) co-operating with the peripheral wall (96) of the jacket (92) and with the piston (91), to define the above-mentioned storage volume (V9). No interstice are present in which the coating fluid could accumulate, thereby making the reservoir (9) easier to clean.