A vibration absorber (10) is provided in a transmission path of a rotary driving force from an engine to a cutter blade and includes: an input-side transmission shaft (11) that receives the rotary driving force from the engine an output-side transmission shaft (12) that is disposed on the same axis (AX) as that of the input-side transmission shaft (11) and is rotatable relative to the input-side transmission shaft (11) to output the rotary driving force to the cutter blade a bushing (13) provided on the axis (AX) and is rotatable relative to the input-side transmission shaft (11) and the output-side transmission shaft (12) a helical torsion coil spring (14) disposed on the axis (AX) and having a first end attached to the bushing (13) and a second end attached to the output-side transmission shaft (12) and a power transmission switching unit (20) that switches a transmission state of the rotary driving force between the input-side transmission shaft (11) and the bushing (13) between a first state and a second state, the first state allowing the transmission of the rotary driving force so that the helical torsion coil spring (14) is deformed in a diameter-reducing range, the second state restricting the transmission of the rotary driving force through the helical torsion coil spring (14).Linvention concerne un amortisseur de vibrations (10) prévu dans un chemin de transmission dune force dentraînement rotative dun moteur à une lame de coupe et comprend : un arbre de transmission côté entrée (11) qui reçoit la force dentraînement rotative du moteur un arbre de transmission côté sortie (12) qui est disposé sur le même axe (AX) que celui de larbre de transmission côté entrée (11) et peut être en rotation par rapport à larbre de transmission côté entrée (11) pour délivrer en sortie la force dentraînement rotative à la lame de coupe une douille (13) prévue sur laxe (AX) et peut tourner par rapport à larbre de transmission côté entrée (11) et larbre de transmission côté s
