To provide a lapping reamer which loses no diameter-adjustable reamer function and inhibits diamonds from being wasted in an undesired site by solving the problem with a conventional reamer wherein diamonds (including borazons) are deposited on a slit section to narrow the width of a slit groove.

The lapping reamer adjusts the diameter of a reamer section by making use of a few lines of slits 10 arranged on the cylindrical reamer section. Granular diamonds 9 or a borazons are temporarily tacked on a reamer base material in a plurality of lines and a plurality of steps with designated intervals by making use of an adhesive between a few lines of slits arranged on the reamer base material, and the diamonds or borazons are firmly fixed by brazing and soldering.