To provide the base installation mechanism of a cutter by which a sufficient tightening force is obtained, even in a comparatively simple structure.

In a base installation mechanism 10 tightening and fixing the main body 2 and base 3 of the cutter such as a jigsaw by a bolt 12, a hole part 13 having a bottom 13a with a nearly V-shaped section is formed inside the main body 2 and a columnar nut member 14 screwed with the bolt 12 is arranged in the hole part 13. By the turning of the nut member 14 along the bottom 13a of the hole part 13, the bolt 12 is moved in the axial direction and the tightening and release of the base 3 with/from the main body 2 is switched.