The collecting mechanism includes a holding unit and a controller. The holding unit has a pair of arms, and can sandwich a machined portion with the pair of arms. The holding unit can be switched between a holding state and a standby state. In the holding state, the pair of arms is closed to be in contact with the circumferential surface of the machined portion to sandwich the machined portion. In the standby state, the pair of arms is opened so as to stay near the circumferential surface of the machined portion with a space between the arms and the circumferential surface of the machined portion. The controller monitors whether cutting-off of the machined portion has been completed to keep the holding unit in the standby state before completion of the cutting-off and to switch the holding unit from the standby state to the holding state at the time of completion of the cutting-off.