PURPOSE: To detect the breakdown of a blade by detecting the vibration of a spindle by fitting an acceleration pickup to a spindle in the blade breakdown detecting mechanism of a dicing saw used at a IC cutting stage.

CONSTITUTION: A magnet is fitted by magnetic force to the lower part of the spindle 3 of a dicing saw. An acceleration pickup 1 is fitted via a screw to the lower part of the magnet 2, the signal line thereof comes in a comparator 5 via an amplifier 4 and connected to a motor driver 6. The motor driver 6 performs the rotation control of a motor 7. The vibration of the spindle 3 is converted into an electric amount by the acceleration pickup 1 and input to the comparator 5 by being amplified by the amplifier 4. In the case a blade 8 is broken down, the vibration of the spindle 3 becomes larger and at the time when the vibration exceeds the threshold value in the comparator 5, an abnormal signal is output to the motor driver 6, which performs the stoppage of the motor 7 and the spindle 3 stops.