polishing slurry 2 a reserved in the slurry supply tank 1 to the slurry feed pump 3 or interrupting a flow of the polishing slurry 2 a fig 5 a description will be given to the operation of the apparatus for polishing a semiconductor device shown in fig5 the ultrasonic transmitting unit 22 generates an ultrasonic wave and transmits the generated ultrasonic wave to the discharged slurry flowing through the discharged slurry pipe 11 via the discharged slurry pipe 11 by closing the discharge valve 12 and the feed valve 17 and opening the recycle valves 13 and 14 the slurry recycle pipe 15 forming the recycle path extending from the discharged slurry pipe 11 to the slurry feed pump 3 is opened in the slurry recycle pipe 15 which has been opened the slurry recycle pump 16 conveys the discharged slurry containing the polishing slurry 2 b under pressure such that it is supplied to the slurry feed pump 3 although the recycled polishing slurry has been supplied directly to the slurry feed pump 3 via the slurry recycle pipe 15 in the foregoing description the present embodiment is not limited thereto it is also possible to provide e g a reservoir for reserving the polishing slurry in a portion of the slurry recycle pipe 15 fig6 shows a structure of the ultrasonic transmitting unit 22 shown in fig5 in fig6 the discharged slurry pipe 11 is installed to pass through pure water 51 filled in a water tab 50 an ultrasonic oscillator 42 generates an ultrasonic wave which is transmitted sequentially through the water tab 50 the pure water 51 and the discharged slurry pipe 11 to the.