BORING TOOL

PROBLEM TO BE SOLVED: To prevent a gap from being generated due to separation of a cartridge surface facing a rear side of a tool rotating direction from the bottom surface of a cartridge mounting seat, the bottom surface facing the tool rotating direction, in adjusting deflection by deflecting the cartridge provided with a cutting edge.SOLUTION: A cartridge mounting seat 6 is formed on an outer periphery of a front end portion of a tool body 1 rotated around an axis O.At a front end portion of a cartridge 7 removably attached to the cartridge mounting seat 6 with the rear end fixed to the seat, a cutting edge 9A projecting toward the outer periphery of the front end portion of the tool body 1 is provided. A deflection adjustment mechanism 11 is provided on the inside of each cartridge mounting seat 6 of the tool body 1, to adjust a projection amount of the cutting edge 9A by deflecting the front end portion of the cartridge 7 toward the outer periphery. A slit 7C is formed between the front end portion and rear end portion of a surface facing the inner periphery side of the cartridge 7, extending from the rear side to the front side of the tool rotating direction, and formed to become gradually deeper toward the front side of the tool rotating direction.