PURPOSE: To improve workability by attaching a saw blade on the flat part of one end of a plunger, providing a fulcrum on a ring shaped member having its inner wall on the outer circumferential part, and providing an action pin which projects from the back side of the flat part and acts as a point of application, a power lever mechanism and a pressing means.

CONSTITUTION: After a knob bolt 8 is moved to the right and one end of a saw blade 3 is inserted into between the flat part 21 of a plunger 2 and the adhesion surface 51 of a set piece 5, the knob bolt 8 is moved to the left and fastened. A fastening force of the knob bolt 8 is transmitted to the pin contact surface 61 of a lever 6, the lever 6 tries to rotate in the anticlockwise direction and the knob bolt contact surface 62 of the lever 6 presses an action pin 4 to the left, and together with a force to pull a boss 52 to the left, the saw blade 3 is fastened between the flat part 21 of the plunger 2 and the adhesion surface 51 of the set piece 5. The saw blade is fastened with a force L/1 times larger than the thread fastening force of a knob bolt 8 according to the principle of a lever. To remove the saw blade 3, it is only necessary to move the knob bolt 8 slightly to the right.