To control the shape of an elastic head at a polishing tool or the like at a real time during processing.

For the elastic tool body section of the polishing tool, both ends of a cylindrical elastic thin film head section 1 is hermetically sealed and retained by a pair of retention plates 2, the elastic thin film head section 1 is maintained in a predetermined external shape by the controllable pressure of a gas supplied from the outside of the device through a gas supply channel 11a provided inside a rotation shaft 11 which is a main tool spindle rotated by a motor 16. The external shape of the elastic thin film head section 1 can be changed in processing according to the local radius of curvature at a lens to be processed W1 by adjusting the distance between the two retention plates 2, 3 by a hydraulic cylinder 19.