A high-frequency antenna of an embodiment is installed on a window of a chamber, and includes first and second antenna elements and first and second relaying portions. The first antenna element extends over a first angle range in a circumferential direction, and the second antenna element extends in the circumferential direction over a second angle range deviating from the first angle range. The second antenna element is arranged away from the window compared to the first antenna element, and is arranged on the outer peripheral side from the first antenna element. The first relaying portion extends toward the side away from the window from the first antenna element, and the second relaying portion extends toward the outer peripheral side, from the first relaying portion to the second antenna element.