A radiation generating apparatus comprising: an envelope having a first window through which a radiation passes; and a radiation tube being held in the envelope and having a second window through which the radiation passes, wherein the first and second windows (2, 15) are arranged in opposition to each other, and wherein the radiation tube comprises: an electron emitting source arranged at an inside of the radiation tube; a target emitting a radiation in response to an irradiation with an electron emitted from the electron source; a substrate having a surface in opposition to the electron emitting source, wherein the target is formed on the surface, and the second window is formed in the substrate; and a radiation shielding member having a first shielding member with an electron beam passing hole in communication with the second window, and a second shielding member with a radiation passing hole in communication with the second window, wherein the first shielding member is configured to protrude from the second window toward the electron emitting source opposite to the second shielding member; the second shielding member is configured to protrude from the second window toward the first window; a thermal conductive member having a thermal conductivity higher than that of the radiation shielding member; and the thermal conductive member is connected at an outer periphery of the second shielding member of the radiation shielding member so as to encircle the second shielding member of the radiation shielding member. an envelope having a first window through which a radiation passes; and a radiation tube being held in the envelope and having a second window through which the radiation passes, wherein the first and second windows (2, 15) are arranged in opposition to each other, and wherein the radiation tube comprises: an electron emitting source arranged at an inside of the radiation tube; a target emitting a radiation in response to an irradiation with an electron emitted from the electron source; a substrate having a surface in opposition to the electron emitting source, wherein the target is formed on the surface, and the second window is formed in the substrate; and a radiation shielding member having a first shielding member with an electron beam passing hole in communication with the second window, and a second shielding member with a radiation passing hole in communication with the second window, wherein the first shielding member is configured to protrude from the second window toward the electron emitting source opposite to the second shielding member; the second shielding member is configured to protrude from the second window toward the first window; a thermal conductive member having a thermal conductivity higher than that of the radiation shielding member; and the thermal conductive member is connected at an outer periphery of the second shielding member of the radiation shielding member so as to encircle the second shielding member of the radiation shielding member. an electron emitting source arranged at an inside of the radiation tube; a target emitting a radiation in response to an irradiation with an electron emitted from the electron source; a substrate having a surface in opposition to the electron emitting source, wherein the target is formed on the surface, and the second window is formed in the substrate; and a radiation shielding member having a first shielding member with an electron beam passing hole in communication with the second window, and a second shielding member with a radiation passing hole in communication with the second window, wherein the first shielding member is configured to protrude from the second window toward the electron emitting source opposite to the second shielding member; the second shielding member is configured to protrude from the second window toward the first window; a thermal conductive member having a thermal conductivity higher than that of the radiation shielding member; and the thermal conductive member is connected at an outer periphery of the second shielding member of the radiation shielding member so as to encircle the second shielding member of the radiation shielding member.