PURPOSE: To prevent a trimmed ear streak part from springing out and rolling in, by interposing an electromagnetic powder clutch in the driving part of pinch rolls and regulating a peripheral speed of the pinch roll.

CONSTITUTION: An ear streak part 5, formed by trimming the side edge part of an aluminum strip material by a trimmer blade 1, is drawn out by pinch rolls 2, cut and processed. The pinch roll 2 interposes an electromagnetic powder clutch 9 between a power transmission chain 7 from a power transmission part and a gear device 8. The electromagnetic powder clutch 9, causing inside a slip, equalizes a peripheral speed of the roll 2 to a feed speed of the strip material. Accordingly, the ear streak part is prevented from its spring out and roll in.