PURPOSE: To shorten replacing time of trimmer cutter by mounting a cutter cartridge dismountably at the end of cutter shaft for fixing cutter.

CONSTITUTION: A trimmer cutter 1 is mounted dismountably at the end of cutter shaft 2 for fixing the cutter, through a spacer 5, such that the tapered section 7a formed on the cartridge shaft 7 of cutter cartridge 6 comprising the cutter 1 and spacer 5 is fitted coaxially and dismountably in the taper hole section 2a of cutter shaft 2. Furthermore a jig is fitted in a hole 23 made in the shaft 7 of cartridge 6 then inserted into the shaft 2 and a piston 13 is retreated to one touch fit the cartridge automatically onto the shaft 2. Consequently replacing time of trimmer cutter can be shortened considerably.