PURPOSE: To improve rigidity and strength of a seat and easily manufacture the seat and a cutter main body.

CONSTITUTION: In a seat fixing construction of a milling cutter, after a seat 30 is brought in close contact with seating faces 21, 22 provided on a milling cutter main body 20, a seat fixing bolt 35 is inserted through a bolt inserting through hole 27 provided on the cutter main body 20, it is screwed in the female screw 31 provided in the seat 30 and fastened, and hence the seat is fixed to the cutter main body 20. Hereby, it is enough that the cutter main body 20 is provided with the bolt inserting through hole 27 and a bolt head receiving recessed part 28, and the seat 30 is provided with the female screw 31, hence rigidity and strength of the seat is improved, and in addition working of the cutter main body 20 and the seat 30 can be easily carried out.