An X-ray tube comprising: an anode target which emits X-rays upon incidence of an electron beam on the anode target; a cathode including a filament (11;13) and a convergence electrode which includes a groove portion in which the filament (11;13) is provided, and which is arranged to cause an electron beam to focus, the electron beam being emitted from the filament (11;13) toward the anode target through an opening of the groove portion, wherein a length direction (da) of the groove portion is a direction along a major axis of the filament (11;13), and a width direction (db) of the groove portion is a direction perpendicular to a depth direction (dc) and the length direction (da) of the groove portion, and the groove portion includes: a pair of first bottom surfaces which are located in the same plane as the filament (11;13) and between which the filament (11;13) is interposed in the width direction (db), and a pair of second bottom surfaces between which the filament (11;13) and the pair of first bottom surfaces are interposed in the length direction (da) and which are located closer to the opening than the pair of first bottom surfaces in the depth direction (dc) to form steps with the first bottom surfaces, wherein the second bottom surfaces are separated from each other in the length direction (da) by the pair of first bottom surfaces, wherein end portions of the filament (11;13) are interposed between the pair of second bottom surfaces in the width direction (db); and an envelope which accommodates the anode target and the cathode. an anode target which emits X-rays upon incidence of an electron beam on the anode target; a cathode including a filament (11;13) and a convergence electrode which includes a groove portion in which the filament (11;13) is provided, and which is arranged to cause an electron beam to focus, the electron beam being emitted from the filament (11;13) toward the anode target through an opening of the groove portion, wherein a length direction (da) of the groove portion is a direction along a major axis of the filament (11;13), and a width direction (db) of the groove portion is a direction perpendicular to a depth direction (dc) and the length direction (da) of the groove portion, and the groove portion includes: a pair of first bottom surfaces which are located in the same plane as the filament (11;13) and between which the filament (11;13) is interposed in the width direction (db), and a pair of second bottom surfaces between which the filament (11;13) and the pair of first bottom surfaces are interposed in the length direction (da) and which are located closer to the opening than the pair of first bottom surfaces in the depth direction (dc) to form steps with the first bottom surfaces, wherein the second bottom surfaces are separated from each other in the length direction (da) by the pair of first bottom surfaces, wherein end portions of the filament (11;13) are interposed between the pair of second bottom surfaces in the width direction (db); and an envelope which accommodates the anode target and the cathode. a pair of first bottom surfaces which are located in the same plane as the filament (11;13) and between which the filament (11;13) is interposed in the width direction (db), and a pair of second bottom surfaces between which the filament (11;13) and the pair of first bottom surfaces are interposed in the length direction (da) and which are located closer to the opening than the pair of first bottom surfaces in the depth direction (dc) to form steps with the first bottom surfaces, wherein the second bottom surfaces are separated from each other in the length direction (da) by the pair of first bottom surfaces, wherein end portions of the filament (11;13) are interposed between the pair of second bottom surfaces in the width direction (db); and an envelope which accommodates the anode target and the cathode.