To micro-adjust the protrusion dimension simply and carry out the replacement easily by providing a protrusion holding mechanism for holding micro-adjustably a ruled line forming protrusion in the vertical direction in the state of setting removably the ruled line-forming protrusion on a top force and also setting the ruled line-forming protrusion thereon.

A top force 4 is disposed fixedly, and a top force base 6 for holding a ruled line-forming protrusion 8 protruded downward is provided, and a ruled line forming protrusion 3 is held removably on the top force base 6, and a protrusion holding mechanism 20 for micro-adjusting the position in the up and down direction is provided. The protrusion holding mechanism 20 is provided with screw sections 3a provided on two positions on the upper section of the ruled line forming protrusion 3, a fitting channel 25a supporting a collar section 22 by a holder 21 fixed on the top force base 6 and fitting the upper section of the ruled line forming protrusion 3 in the fitting channel and a supporting screw section 23 screwed with the screw section 3a. The micro-adjustment for the ruled line forming protrusion 3 in the vertical direction is carried out by inserting a hexagonal wrench or the like into a hexagonal socket 30 on the upper face of a screw 24 and turning over the same.