PURPOSE: To guarantee smooth flow of chips by making an insert hole accommodating a lock pin a blind hole in a pin lock system for retaining a cutting edge insert in a tool holder.

CONSTITUTION: The shaft of a lock pin 12 is inserted in a lock pin accommodating hole 11 of a tool holder 10, and a cutting edge insert 19 is contacted with a bottom surface and a side-wall surface of an insert accommodating pocket 23 of the holder 10, and also the head 13 of the lock pin 12 is fitted in a central blind hole 16 of the insert 19. Thus, a projecting lip 14 of the head 13 is engaged with a cone-shaped surface 15 of the blind hole 16. Thereafter, a working screw 20 is engaged with a recess part 22 of the lock pin 12 and tightened, then the lock pin 12 is moved downward along inclination of the accommodating hole 11, also the insert 19 is strongly tightened to the tool holder 10 by the projecting lip 14. Therefore, the flow of chips cut by a cutting edge 25 becomes smooth, and the adhering of the cutting edge 25 material can be strengthened.