A processing device includes a mounting base, a cutter holder, and a brake. The brake includes a driving member, a resisting member, and an elastic member. The driving member includes a main body and a driving shaft movably placed in the main body. The driving shaft is driven to move in a straight line by the main body. One end of the driving shaft is movably coupled to the cutter holder, and another end of the driving shaft is coupled to the resisting member. The elastic member is positioned between the main body and the resisting member. The driving shaft is configured to move toward one side of the driving member adjacent to the elastic member under an elastic restoring force of the elastic member, whereby the cutter holder moves with the driving shaft toward one end of the driving member adjacent to the elastic member.