PURPOSE: To provide an X-ray generating device of rotary counter-cathode type which can be carried freely upon a table and which can be installed in any desired place on the table.

CONSTITUTION: An X-ray generating device concerned comprises a casing 1 in which an electron gun 2 and target 3 positioned opposingly are accommodated airtightly, a target body part 7 in which a motor for rotating the target 3 is accommodated, a power lead-in terminal 4 to supply electric power to the gun 2 and target 3. and an air exhaust pump 18 to decompress the inside of the casing 1. The body part 7, terminal 4, and pump 18 are secured to the casing 1 in positions over a table 6. Because this table 6 should not necessarily be provided with a hole for allowing running-off of any part protruding at the casing 1 such as the terminal 4, it is practicable to carry simply the X-ray generating device 12 upon the table 6 and to locate and fix in any desired place.