To carry out a centerless grinding applied to a cylindrical surface form to be machined (a valve stem, for example) and a conical surface form to be machined (a valve face, for example), which are formed in a workpiece (a valve for internal combustion engine, for example), simultaneously and in an adequate grinding condition so that a salient slip between a regulating wheel and the workpiece is not caused.

Of parts to be machined at two positions, one side part to be machined (a valve stem 31a) is rotated while holding it by a single regulating wheel 10' and a bladed (both are concealed). The cylindrical surface form to be machine (the valve stem 31a) is centerless ground by the first grinding wheel 7', while a conical surface form to be machined (a valve face 31b) is centerless ground by the second grinding wheel 8'. The peripheral speeds of the first and the second grinding wheels 7' and 8' are controlled independently each other.