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).
