The method and apparatus are provided for preparing a slurry for a CMP apparatus with which mixing accuracy for a slurry is improved and accurate measurement is automatically accomplished for H₂O₂ as a small amount of additive. A slurry preparation apparatus for a CMP apparatus comprises a tank for preparing the slurry, a stock solution feeder for the slurry which feeds a stock solution for the slurry into the tank, and a concentration measurement instrument located outside the tank, which is capable of measuring an additive concentration in the slurry in the tank. The concentration measurement instrument measures the additive concentration in the slurry in the tank, and the amount of the stock solution for the slurry to be supplied is controlled according to the measurements.