A polishing apparatus is provided for accurately detecting the relative displacement between an upper wheel and a lower wheel and thus for reliably polishing workpieces to a desired thickness. The polishing apparatus includes an upper wheel for pressing at least one workpiece, a lower wheel for supporting the workpiece, non-contact-type displacement-detection device for detecting the relative displacement between the upper wheel and the lower wheel, and a reference table for providing a displacement-detection reference position. The non-contact-type displacement-detection device is joined to the upper wheel so as to move therewith. The reference table is disposed at a position opposing the displacement-detection device and also is integrally connected to the lower wheel.