PURPOSE: To easily mount and demount a saw blade.

CONSTITUTION: The shaft part 37a of a holder 37 is inserted into an upper part slide shaft 34. A knob 40 is installed in slidable manner at the edge part of the holder 37. A coil spring 43 is interposed between the knob 40 and the upper part slide shaft 34, and the knob 40 is energized in the direction separating from the upper part slide shaft 34. A hollow part 37e which communicates to a blade insertion hole 37d is formed on the holder 37, and the side wall is formed to a tapered surface part 37f. A slot hole 40a is formed on the knob 40, and the edge part of a roller 42 is inserted into the slot hole 40a, and supported. The roller 42 is accommodated into the hollow part 37e, and pressed to the tapered surface part 37f.