A bending state known as “coning,” in which the amount of bending of the flexspline gradually decreases in accordance with the distance from the open end of the spline, occurs in cup-type or “silk hat”-type wave gear devices. A tooth profile in which the tooth depth is kept constant and in which the bottom lands and top lands are parallel to each other along the tooth trace direction is used as the basic tooth profile for the circular spline and the flexspline of the wave gear device. A taper surface is formed on a part of the top land near the open end of the flexspline in the basic tooth profile, whereby a modified tooth profile is obtained. The modified tooth profile is employed as the tooth profile for both of the splines. Both of the splines can be caused to mesh together without generating coning-induced interference. Both of the splines can also be subjected to gear cutting by a simple process using a typical machining mechanism.