PURPOSE: To autmatically detect a blocked ear when a side-trimmed ear piece is treated with the use of a chopper, by comparing a fluctuating period of torsional torque generated in the shaft of a rotary blade cutter with the cutting period of a chopper so that whether both periods correspond together or not is discriminated.

CONSTITUTION: A strain guage 10 is applied to a suitable position on a shaft 9 to which the rotary blade cutter 7 of a chopper is journalled, and an FM telemeter antenna 11 is arranged in opposite to the strain guage 10, which is connected to a telemeter 12 for detecting torsional torque. A drive motor 13 for the shaft 9 is attached with a pulse generator 14 for detecting the rotational speed of the shaft 9 as pulse signals which are counted by a counter 15. A time-calculating circuit 16 which receives a signal from the cunter 15, calculates a sampling time and delivers its signal to a discriminating circuit which receives a torsional torque signal from the telemeter 12 and signals for indicating the operation or rest of the line. The number of pulses from the telemeter 12 are counted within the sampling time upon the operation of the line, thereby whether a blocked ear is occured or not is discriminated.