Crop cutting device (17) comprising knives (18) pivotally mounted below a crop guiding surface (22). Each knife (18) is pivotable between a retracted position in which it is located below the guiding surface (22) and an extended position, wherein at least a cutting edge (25) of the knife (18) projects above the surface (22). A selector mechanism (72) is foreseen for selectively holding spring loaded parts (32) of operating members (31) to maintain the corresponding knife (18) in its retracted inoperative position while the operating member (31) is moved to its second position；Therefore, the selector mechanism (72) includes a shaft (49) carrying a plurality of cam elements (50A-F) which are substantially parallel, individually mounted on the shaft (49) and arranged to be moved to a position for blocking a respective spring loaded part (32) upon rotation of the shaft (49) from a non-holding to a holding position.
