To provide a method and a device for manufacturing a cathode structure of an X-ray tube capable of setting a cathode filament to the correct position.

Positioning parts 20a, 20b to determine the position of a cathode filament of an X-ray tube are provided in a projected manner, and two positioning blocks 18a, 18b in which flat surfaces 19a, 19b in the vicinity of the positioning parts 20a, 20b are intersected with each other at the prescribed angle, an elastic body 21 to support the positioning blocks 18a, 18b, and a pressing mechanism 22 to apply the force to closely attach surfaces 13a, 13b surrounding forcusing grooves of a forcusing body for the X-ray tube on which the cathode filament 16 is provided to the flat surfaces 19a, 19b of the positioning blocks 18a, 18b, are provided.