A PCVD apparatus includes a waveguide member which supports the workpiece with a portion of the waveguide member positioned in a reactor and causes microwaves output from a high-frequency output device to propagate to the workpiece. In a process of gradually increasing an intensity of the microwaves propagating to the workpiece through the waveguide member from “0”, the intensity of the microwaves output from the high-frequency output device when step-up of a bias current of the workpiece occurs is referred to as a first intensity, and in a process of gradually increasing the intensity of the microwaves from the first intensity, the intensity of the microwaves when step-up of the bias current occurs again is referred to as a second intensity. During film formation, the microwaves having an intensity of higher than the first intensity and lower than the second intensity are output from the high-frequency output device.