A synchronizing device for a transmission comprising: a hub provided on an outer circumference of a rotation shaft and configured to integrally rotate with the rotation shaft; a gear disposed on a side or both sides of the hub and configured to rotate relative to the rotation shaft; an annular sleeve which is provided on an outer circumference of the hub, includes on an inner circumference thereof a spline that restricts the sleeve from rotating relative to the hub but allows the sleeve to move in an axial direction, and is configured to couple with the gear by moving along the axial direction to mesh the spline with a spline formed on the gear; and an annular synchronizer ring which is disposed between the hub and the gear, includes on an outer circumference thereof a spline, and is assembled so as to rotate relative to the hub by a predetermined angle, wherein a chamfer (25, 35) is provided on each of ends of the spline of the sleeve and the spline of the gear that face each other, and is also provided on an end, close to the hub, of the spline of the synchronizer ring, each spline of the sleeve has a pair of chamfers symmetrically provided about the center line of the spline perpendicular to the width direction, and distal ridges of the pair of chamfers are inclined such that the radially outer portion projects toward the gear, a distal end of the chamfer of the synchronizer ring has a first chamfer in a radially outer side of a boundary ridge and a second chamfer in a radially inner side of a boundary ridge, and is formed in a trapezoidal shape in a plan view and in a side view perpendicular to a plane normal to a rotation axis, the boundary ridge is a boundary between the first chamfer and the second chamfer and is provided at a predetermined height from a root of the spline of the synchronizer ring, a balk radius at which a ridge angle of a chamfer of the synchronizer ring changes is set larger than an inner radius of the sleeve, so that the vicinity of the intersection of the ridge of the first chamfer and the ridge of the second chamfer and the boundary ridge is brought into contact with the chamfer of the sleeve, the ridge angle (a) of the first chamfer of the synchronizer ring is larger than a ridge angle (y) of the chamfer of the sleeve, the ridge angle (β) of the second chamfer of the synchronizer ring is smaller than the ridge angle (y) of the chamfer of the sleeve, characterized in that the first chamfer is formed by three faces (45a, 43, 45a) and having boundaries of the three faces as ridges (46,46), the second chamfer is formed by three faces (45b, 43, 45b) and having boundaries of the three faces as the ridges (46, 46), and has a smaller ridge angle (β) than a ridge angle (α) of first chamfer. a hub provided on an outer circumference of a rotation shaft and configured to integrally rotate with the rotation shaft; a gear disposed on a side or both sides of the hub and configured to rotate relative to the rotation shaft; an annular sleeve which is provided on an outer circumference of the hub, includes on an inner circumference thereof a spline that restricts the sleeve from rotating relative to the hub but allows the sleeve to move in an axial direction, and is configured to couple with the gear by moving along the axial direction to mesh the spline with a spline formed on the gear; and an annular synchronizer ring which is disposed between the hub and the gear, includes on an outer circumference thereof a spline, and is assembled so as to rotate relative to the hub by a predetermined angle, wherein a chamfer (25, 35) is provided on each of ends of the spline of the sleeve and the spline of the gear that face each other, and is also provided on an end, close to the hub, of the spline of the synchronizer ring,