Abstract: A process for producing diamond includes a step of bringing a columnar cathode and a tubular pilot anode provided concentrically around the cathode, into proximity to a plasma jetting port of a front end portion of a tubular main anode provided concentrically around the pilot anode. According to the process, a voltage is applied across the cathode and the pilot anode to convert a pilot gas to the form of a plasma. Then, the cathode is moved away from the pilot anode along a common axis. The process also includes the step of holding the discharge voltage between the cathode and the pilot anode at a first preselected voltage, and then applying voltage across the cathode and the main anode to convert a main gas to the form of a plasma. Subsequently, at least the pilot anode is moved away from the main anode along the common axis while maintaining the discharge voltage between the cathode and the pilot anode at the first preselected voltage.