An X-ray tube comprising: an anode target configured to radiate X-rays by incidence of an electron beam; a cathode comprising an electron emission source (11,12,13) configured to emit electrons, and a converging electrode including a trench portion (16,17,18) accommodating the electron emission source (11,12,13), and configured to converge the electron beam towards the anode target through an opening (16a,17a,18a) of the trench portion (16,17,18) as the electrons are emitted from the electron emission source (11,12,13), and a vacuum envelope accommodating the anode target and the cathode, wherein the trench portion comprises: a closest inner circumferential wall extending in a depth direction (dc) of the trench portion, having a dimension shorter than the dimension of the electron emission source in the depth direction (dc) of the trench portion, and facing the electron emission source with a gap (yb) in a width direction (db) of the trench portion, an upper inner circumferential wall located on the opening side of the trench portion with respect to the closest inner circumferential wall and having a shape widening in the width direction (db) further from the closest inner circumferential wall, and a lower inner circumferential wall located on an opposite side to the upper inner circumferential wall with respect to the closest inner circumferential wall and having a shape widening in the width direction (db) further from the closest inner circumferential wall, characterized in that the electron emission source projects towards the opening side of the trench portion beyond a position in the depth direction (dc) of the trench portion defined by the location of the boundary between the closest inner circumferential wall and the upper inner circumferential wall in the depth direction (dc) of the trench portion. an anode target configured to radiate X-rays by incidence of an electron beam; a cathode comprising an electron emission source (11,12,13) configured to emit electrons, and a converging electrode including a trench portion (16,17,18) accommodating the electron emission source (11,12,13), and configured to converge the electron beam towards the anode target through an opening (16a,17a,18a) of the trench portion (16,17,18) as the electrons are emitted from the electron emission source (11,12,13), and a vacuum envelope accommodating the anode target and the cathode, a closest inner circumferential wall extending in a depth direction (dc) of the trench portion, having a dimension shorter than the dimension of the electron emission source in the depth direction (dc) of the trench portion, and facing the electron emission source with a gap (yb) in a width direction (db) of the trench portion, an upper inner circumferential wall located on the opening side of the trench portion with respect to the closest inner circumferential wall and having a shape widening in the width direction (db) further from the closest inner circumferential wall, and a lower inner circumferential wall located on an opposite side to the upper inner circumferential wall with respect to the closest inner circumferential wall and having a shape widening in the width direction (db) further from the closest inner circumferential wall, characterized in that the electron emission source projects towards the opening side of the trench portion beyond a position in the depth direction (dc) of the trench portion defined by the location of the boundary between the closest inner circumferential wall and the upper inner circumferential wall in the depth direction (dc) of the trench portion.