An X-ray generating tube comprising: a transmission target having a first surface and a second surface opposite to the first surface , an anode member configured to form an anode with the transmission target , an electron emitting source arranged to emit an electron beam and irradiate the first surface with the electron beam obliquely, a cathode member configured to form a cathode with the electron emitting source , an insulating tube configured to form a vacuum container with the anode and the cathode , and a hollow shield member secured to the anode member and holding the transmission target therein configured to shield a part of X-rays generated at the transmission target , wherein the hollow shield member has a tubular backward shield member and a hollow forward shield member located at a first surface side and a second surface side of the transmission target respectively, characterized in that , the backward shield member having an electron beam passage through which the electron beam passes and being secured to the anode member such that the backward shield member has a protruding portion which produces outwards beyond the anode member and the transmission target is held at the protruding portion, the hollow forward shield member has a radiation opening configured to define a radiation angle (Λ), an exit angle (φ) and an azimuth angle (ψ) of the X-ray beam partially passed through, and the exit angle (φ) and the azimuth angle (ψ) are defined by the radiation opening such that the projection of the central axis of the electron beam and of the central axis of the X-ray beam onto the first surface of the transmission target are in an antiparallel vector relationship with each other. a transmission target having a first surface and a second surface opposite to the first surface , an anode member configured to form an anode with the transmission target , an electron emitting source arranged to emit an electron beam and irradiate the first surface with the electron beam obliquely, a cathode member configured to form a cathode with the electron emitting source , an insulating tube configured to form a vacuum container with the anode and the cathode , and a hollow shield member secured to the anode member and holding the transmission target therein configured to shield a part of X-rays generated at the transmission target , wherein the hollow shield member has a tubular backward shield member and a hollow forward shield member located at a first surface side and a second surface side of the transmission target respectively, characterized in that , the backward shield member having an electron beam passage through which the electron beam passes and being secured to the anode member such that the backward shield member has a protruding portion which produces outwards beyond the anode member and the transmission target is held at the protruding portion, the hollow forward shield member has a radiation opening configured to define a radiation angle (Λ), an exit angle (φ) and an azimuth angle (ψ) of the X-ray beam partially passed through, and the exit angle (φ) and the azimuth angle (ψ) are defined by the radiation opening such that the projection of the central axis of the electron beam and of the central axis of the X-ray beam onto the first surface of the transmission target are in an antiparallel vector relationship with each other. <EOS>