A plasma processing apparatus including a vacuum chamber, a gas supply unit for supplying gas into the vacuum chamber, an exhausting unit for exhausting the interior of the vacuum chamber, a pressure-regulating valve for controlling the interior of the vacuum chamber to a specified pressure, a substrate electrode for placing thereon a substrate within the vacuum chamber, an antenna provided opposite to the substrate electrode, and a high-frequency power supply capable of supplying to the antenna a high-frequency power having a frequency of 50 MHz to 3 GHz. The plasma processing apparatus also has a dielectric plate sandwiched between the antenna and an inner surface of the vacuum chamber, an antenna cover for covering side surfaces of the antenna and the dielectric plate and a substrate-facing surface of the antenna, a slit cover for covering an exposed surface of the substrate-facing inner surface of the vacuum chamber and fixing the antenna cover to a wall surface of the vacuum chamber. Also, a heat-conducting sheet is provided between the antenna and the antenna cover.