The wheelchair comprises a seat back a module (2) movably coupled to a seat module (5). Two lateral plates (10, 10′) are secured to the seat back module (2) and pivotally mounted on the seat module (5). Each of said plate is provided with a recess (18, 18′) adapted to lodge an excenter member (19) comprising two parallel side faces (26, 27) and being perforated by three holes (21, 22 and 23), adapted to receive a spring release locking pins for locking the angle position of said seat back module. Due to the positioning of said three holes and the possibility of lodging the excenter member with either one of its two side faces (26 or 27) inside the recess (18), five different locking angle positions of the seat back module are possible.