When a work W rotates counterclockwise about an axis Ow and is subjected to infeed grinding by a regulating wheel (1) which rotates clockwise about an axis O1 and a grinding wheel (2) which rotates clockwise about an axis O2, a load F acting on a blade (4), a load acting on the work W supported by the blade (4), and a load operating position y in the blade (4) at any given time are measured by a controller (20) based on the outputs of a first stress sensor S1 and a second stress sensor S2 and according to the correlation information stored in a storage device. If the component of a specified frequency extracted by performing frequency analysis of the time series of the load exceeds a threshold value, then designation processing is carried out to reduce the component of the designated frequency to the threshold value or less.