PROBLEM TO BE SOLVED: To provide a plasma device using arc discharge capable of continuing spark-less discharge.SOLUTION: A plasma device 10 comprises a vacuum container 1, a cathode flange 5, a magnet 7, a negative electrode member 8, a trigger electrode 11, and a power source 14. The cathode flange 5 is fixed to a side wall of the vacuum container 1 opposite to a substrate 20. The negative electrode member 8 is made of laminate carbon or glassy carbon, and is mounted to the cathode flange 5. The power source 14 applies negative voltage to the cathode flange 5. The magnet 7 applies an axial magnetic field having a magnetic field component in a normal direction of the negative electrode member 8 larger than a magnetic field component in an in-plane direction of the negative electrode member 8 to the negative electrode member 8. While an axial magnetic field is applied to the negative electrode member 8 by the magnet 7, the trigger electrode 11 is brought into contact with the negative electrode member 8 and arc discharge is started, so as to form a carbon thin film on the substrate 20.