A rotary blade (A) for use in a lawn mower, said rotary blade being provided with the following: a retention member (100) that is attached to an attachment shaft (14) and rotated and a cord-shaped cutting member (4a), the base end of which is held inside the retention member (100). The retention member (100) is provided with a main body (100a) coupled to the attachment shaft (14), manipulable parts (100b) that hold the base end of the cord-shaped cutting member in a wound manner, and a clutch mechanism (160). The manipulable parts (100b) are combined so as to be manipulable so as to produce relative rotation and movable, as part of a prescribed stroke, in the axial direction of the attachment shaft (14) relative to the main body (100a). The clutch mechanism (160) prevents relative rotation between the manipulable parts (100b) and the main body (100a) when the manipulable parts (100b) are at a given position in the aforementioned stroke as a result of the elastic restoring force of an elastic member (150), but permits relative rotation between the manipulable parts (100b) and the main body (100a) when the manipulable parts (100b) have been moved from said given position against the elastic restoring force of the elastic member (150).La présente invention concerne une lame rotative (A) devant être utilisée dans une tondeuse à gazon. Ladite lame rotative est dotée des éléments suivants : un élément de retenue (100) qui est fixé à un arbre de fixation (14) et mis à tourner et un élément de coupe en forme de cordon (4a) dont lextrémité de base est maintenue à lintérieur de lélément de retenue (100). Lélément de retenue (100) est doté dun corps principal (100a) accouplé à larbre de fixation (14), de pièces manipulables (100b) qui tiennent lextrémité de base de lélément de coupe en forme de cordon dune façon enroulée, et dun mécanisme dembrayage (160). Les pièces manipulables (100b) sont combinées de façon à pouvoir être manipulées pour produire une rotation relative et s
