PURPOSE: To remove sludge adhered to anode and raise the cooling efficiency of X-ray tube by providing a device by which a granular substance is mixed into and recovered from a circulation path for a cooling liquid to be sprayed onto the anode of an X-ray tube.

CONSTITUTION: The inflow path A through which the insulation oil 5 is sucked up by the pump 3 to cool an X-ray tube 2 and then circulated through the heat exchanger 9 is provided with the branched path A1 having the granule-housed filter 22 in which the glass grains 22a, etc., are placed on the net 22a and the stop valve 21, and also the recovery path B is provided with the branched path B1 having the stop valve 23 and the recovery filter 24. And, by switching the stop valves 20, 21 and 8, 23, the grains 22a are mixed into the insulation oil 5 and then recovered by the filter 24. Thus, sludge adhered to the anode of the X-ray tube 2 is easily removed by the action of the grains 22a and the cooling efficiency can therefore be raised.