A gear grinding unit (4A, 4B, 4C) comprising: a threaded grinding part (8A, 8B, 8C) that is rotatable around a rotation axis (S 1) and engages with a tooth of a gear to be ground, wherein a tooth flank of the gear is ground through a rotational motion of the threaded grinding part (8A, 8B, 8C), the gear grinding unit (4A, 4B, 4C) being characterized by: a plurality of flexible abrasive sheets (10A, 10B, 10C, 10D) each including a bulge part bulging radially outward from a virtual circle whose diameter equals a root diameter (D A) of the threaded grinding part (8A, 8B, 8C), wherein a curved part outlining the bulge part includes a first curved part such that, in a first predetermined angle region around a center point (O 1) of the virtual circle, a distance from the center point to the first curved part increases as an angle around the center point (O 1) increases, and a second curved part such that, in a second predetermined angle region adjoining the first predetermined angle region, a distance from the center point to the second curved part decreases as an angle around the center point (O 1) increases, wherein the threaded grinding part (8A, 8B, 8C) is formed by overlapping the plurality of abrasive sheets (10A, 10B, 10C, 10D) along the rotation axis (S 1) with the bulge parts of the abrasive sheets (10A, 10B, 10C, 10D) mutually shifted by a predetermined angle around the rotation axis, and wherein, when the threaded grinding part (8A, 8B, 8C) is pressed against the tooth of the gear, the abrasive sheets (10A, 10B, 10C, 10D) bend according to a profile of the tooth to allow a thread of the threaded grinding part (8A, 8B, 8C) to be in close contact with the tooth flank. a threaded grinding part (8A, 8B, 8C) that is rotatable around a rotation axis (S 1) and engages with a tooth of a gear to be ground, wherein a tooth flank of the gear is ground through a rotational motion of the threaded grinding part (8A, 8B, 8C), the gear grinding unit (4A, 4B, 4C) being characterized by: a plurality of flexible abrasive sheets (10A, 10B, 10C, 10D) each including a bulge part bulging radially outward from a virtual circle whose diameter equals a root diameter (D A) of the threaded grinding part (8A, 8B, 8C), wherein a curved part outlining the bulge part includes a first curved part such that, in a first predetermined angle region around a center point (O 1) of the virtual circle, a distance from the center point to the first curved part increases as an angle around the center point (O 1) increases, and a second curved part such that, in a second predetermined angle region adjoining the first predetermined angle region, a distance from the center point to the second curved part decreases as an angle around the center point (O 1) increases, wherein the threaded grinding part (8A, 8B, 8C) is formed by overlapping the plurality of abrasive sheets (10A, 10B, 10C, 10D) along the rotation axis (S 1) with the bulge parts of the abrasive sheets (10A, 10B, 10C, 10D) mutually shifted by a predetermined angle around the rotation axis, and wherein, when the threaded grinding part (8A, 8B, 8C) is pressed against the tooth of the gear, the abrasive sheets (10A, 10B, 10C, 10D) bend according to a profile of the tooth to allow a thread of the threaded grinding part (8A, 8B, 8C) to be in close contact with the tooth flank. a plurality of flexible abrasive sheets (10A, 10B, 10C, 10D) each including a bulge part bulging radially outward from a virtual circle whose diameter equals a root diameter (D A) of the threaded grinding part (8A, 8B, 8C), wherein a curved part outlining the bulge part includes a first curved part such that, in a first predetermined angle region around a center point (O 1) of the virtual circle, a distance from the center point to the first curved part increases as an angle around the center point (O 1) increases, and a second curved part such that, in a second predetermined angle region adjoining the first predetermined angle region, a distance from the center point to the second curved part decreases as an angle around the center point (O 1) increases, wherein the threaded grinding part (8A, 8B, 8C) is formed by overlapping the plurality of abrasive sheets (10A, 10B, 10C, 10D) along the rotation axis (S 1) with the bulge parts of the abrasive sheets (10A, 10B, 10C, 10D) mutually shifted by a predetermined angle around the rotation axis, and wherein, when the threaded grinding part (8A, 8B, 8C) is pressed against the tooth of the gear, the abrasive sheets (10A, 10B, 10C, 10D) bend according to a profile of the tooth to allow a thread of the threaded grinding part (8A, 8B, 8C) to be in close contact with the tooth flank.