PURPOSE: To facilitate selecting a blade-forming abrasive particle material optimum for an object and selecting machining conditions such as feeding speed of a blade and depth of a groove, by securely grasping machining resistance at the time of machining such as cutting-off.

CONSTITUTION: A circuit drawing for measuring as electric power a load on a motor for a blade spindle shows a three-phase motor 6, a transducer 7 for measuring load electric power on the motor 6, a panel meter 8 for measuring the output of the transducer 7, an electric current input terminal 9 and a voltage terminal 10 for the transducer 7 and the like. Actual machining resistance exerted on the blade spindle at the time of cutting-off machining is grasped as electric power, and can be proportionally displayed on the panel meter 8. Accordingly, selection of a blade-forming abrasive particle material optimum for the object to be machined and selection of machining conditions such as feeding speed of the blade and depth of a groove can be facilitated.