The mower has a frame (4) carrying a leg (5) on which a cuter bar (2) is articulated. An unfolding and folding device (3) moves the bar from an operation configuration into a transport configuration and vice-versa. The device has a tilting unit (7) connected to the leg and the frame, a connecting rod (8) connected to the bar, and a double-acting jack (6) positioned between the unit (7) and the rod.