PURPOSE: To make a control circuit or the like unnecessary, and stabilize the pulse width and the pulse dose by making a conversion layer which is used for X-ray conversion and located on the focus forming surface of a rotary anode, such as a heavy-metal layer, discontinuous in the rotational direction of the anode so as to prevent any X-ray conversion from being carried out at the gaps of the said heavy-metal layer.

CONSTITUTION: An anode (P) is prepared from a truncated-cone-shaped base 21 made of a non-heavy-metal member, and a heavy-metal layer 22 is formed on the side surface of the truncated cone 21. In addition, parts 23 and 23', which are indicated in the figure and are located on loci facing to the cathode, are removed so as to make parts of the heavy-metal layer 22 to be removed, or a plural number of (only one will do) straight fluted grooves 24, 24', 25, 25' and 25" as indicated in the figure are regularly formed so as to make the regularly arranged parts of the heavy metal layer 22 to be removed. As a result, a stable X-ray pulse with a good quality is obtained only by discharging an electron beam while rotating the anode (P).