A reamer comprising: an attaching portion removably attached to a shank; a cutting portion having a core portion and a surface portion covering the core portion around a central axis; and a joint portion that joins the attaching portion and the cutting portion, the core portion including a cemented carbide material, the surface portion including PCD or CBN, the surface portion including a groove, a flank face, and a cutting edge formed by a ridgeline between the groove and the flank face, the cutting edge extending from the end toward the attaching portion, the reamer being characterized by: the attaching portion consisting of a hard material including a hard component and a metal binder, the hard component being at least one selected from the group consisting of TiC, TiCN, W, WC, Al 2 O 3, and a combination of at least one of CBN and diamond and at least one of W and WC, the metal binder including one or two or three of Fe, Ni and Co, the hard material having a Young's modulus of not more than 350 GPa, the cutting portion having a chamfer portion located at an end thereof opposite to the attaching portion, the flank face being formed of a chamfer flank face located at the chamfer portion, and an outer circumferential flank face located at a portion other than the chamfer portion, inclination of the chamfer flank face with respect to the central axis being greater than inclination of the outer circumferential flank face with respect to the central axis. an attaching portion removably attached to a shank; a cutting portion having a core portion and a surface portion covering the core portion around a central axis; and a joint portion that joins the attaching portion and the cutting portion, the core portion including a cemented carbide material, the surface portion including PCD or CBN, the surface portion including a groove, a flank face, and a cutting edge formed by a ridgeline between the groove and the flank face, the cutting edge extending from the end toward the attaching portion, the reamer being characterized by: the attaching portion consisting of a hard material including a hard component and a metal binder, the hard component being at least one selected from the group consisting of TiC, TiCN, W, WC, Al 2 O 3, and a combination of at least one of CBN and diamond and at least one of W and WC, the metal binder including one or two or three of Fe, Ni and Co, the hard material having a Young's modulus of not more than 350 GPa, the cutting portion having a chamfer portion located at an end thereof opposite to the attaching portion, the flank face being formed of a chamfer flank face located at the chamfer portion, and an outer circumferential flank face located at a portion other than the chamfer portion, inclination of the chamfer flank face with respect to the central axis being greater than inclination of the outer circumferential flank face with respect to the central axis. the attaching portion consisting of a hard material including a hard component and a metal binder, the hard component being at least one selected from the group consisting of TiC, TiCN, W, WC, Al 2 O 3, and a combination of at least one of CBN and diamond and at least one of W and WC, the metal binder including one or two or three of Fe, Ni and Co, the hard material having a Young's modulus of not more than 350 GPa, the cutting portion having a chamfer portion located at an end thereof opposite to the attaching portion, the flank face being formed of a chamfer flank face located at the chamfer portion, and an outer circumferential flank face located at a portion other than the chamfer portion, inclination of the chamfer flank face with respect to the central axis being greater than inclination of the outer circumferential flank face with respect to the central axis.