A torque-transmission joint is configured to transmit torque between one axial end portion of a drive shaft and the other axial end portion of a driven shaft arranged in series with each other in an axial direction, the torque-transmission joint comprising: a coupling (20, 20a, 20b, 20c, 20e) provided on one circumferential surface of inner and outer circumferential surfaces with a coupling-side concave-convex portion (35, 35a) having coupling-side convex portions (34, 34a) arranged at a plurality of circumferential places and protruding in a radial direction; a drive-side transmission part provided at one axial end portion of the drive shaft and is provided on one circumferential surface, which faces the coupling-side concave-convex portion (35, 35a), of inner and outer circumferential surfaces with a drive-side concave-convex portion having drive-side convex portions arranged at a plurality of circumferential places and protruding in a radial direction; and a driven-side transmission part provided at the other axial end portion of the driven shaft and is provided on one circumferential surface, which faces the coupling-side concave-convex portion (35, 35a), of inner and outer circumferential surfaces with a driven-side concave-convex portion having driven-side convex portions arranged at a plurality of circumferential places and protruding in a radial direction; wherein circumferential rigidity of both axial end portions of each coupling-side convex portion (34, 34a) is lower than circumferential rigidity of an axially intermediate portion of each coupling-side convex portion (34, 34a), wherein the drive-side concave-convex portion is engaged with a half portion on the other axial side of the coupling-side concave-convex portion (35, 35a), and the driven-side concave-convex portion is engaged with a half portion on one axial side of the coupling-side concave-convex portion (35, 35a), characterized in that both axial end portions of each coupling-side convex portion (34, 34a) are provided with a thickness-reduced portion opening into both axial end surfaces of each coupling-side convex portion (34, 34a) and an outer peripheral surface of the coupling (20, 20a, 20b, 20c, 20e). a coupling (20, 20a, 20b, 20c, 20e) provided on one circumferential surface of inner and outer circumferential surfaces with a coupling-side concave-convex portion (35, 35a) having coupling-side convex portions (34, 34a) arranged at a plurality of circumferential places and protruding in a radial direction; a drive-side transmission part provided at one axial end portion of the drive shaft and is provided on one circumferential surface, which faces the coupling-side concave-convex portion (35, 35a), of inner and outer circumferential surfaces with a drive-side concave-convex portion having drive-side convex portions arranged at a plurality of circumferential places and protruding in a radial direction; and a driven-side transmission part provided at the other axial end portion of the driven shaft and is provided on one circumferential surface, which faces the coupling-side concave-convex portion (35, 35a), of inner and outer circumferential surfaces with a driven-side concave-convex portion having driven-side convex portions arranged at a plurality of circumferential places and protruding in a radial direction; wherein circumferential rigidity of both axial end portions of each coupling-side convex portion (34, 34a) is lower than circumferential rigidity of an axially intermediate portion of each coupling-side convex portion (34, 34a), wherein the drive-side concave-convex portion is engaged with a half portion on the other axial side of the coupling-side concave-convex portion (35, 35a), and the driven-side concave-convex portion is engaged with a half portion on one axial side of the coupling-side concave-convex portion (35, 35a),