Electron gun, X-ray generation apparatus, and X-ray imaging apparatus

An electron gun comprising a cathode including an electron emitting portion, an extraction electrode configured to extract electrons emitted from the electron emitting portion, and a focusing electrode configured to focus the electrons extracted by the extraction electrode, wherein

• the focusing electrode includes an outside electrode having a tubular shape, and an inside electrode arranged inside the outside electrode so as to be surrounded by the outside electrode, the inside electrode defines a first space having a columnar shape, and includes a first surface on a side of the cathode, and a second surface on an opposite side of the first surface, and an inside surface of the outside electrode and the second surface of the inside electrode define a second space, and
• the inside electrode includes an electron passage hole through which the electrons pass, and a communicating portion arranged apart from the electron passage hole and configured to make the first space and the second space communicate with each other.