The utility model relates to an angle adjusting device. A locking toothed plate and a fixed seat are fixedly connected on a rotary shaft, a diaphragm spring is positioned between the front end face of the locking toothed plate and the inner end face of the fixed seat, an unlocking handle is installed on the rotary shaft extending out of the fixed seat, a boss is positioned in an inner hole of the unlocking handle, and the boss is clamped in a rotary groove on the left of the rotary shaft. In a locking state, the locking toothed plate is in meshed connection with an inner tooth of an inner toothed ring. The locking toothed plate and the rotary shaft are in matched connection through the boss and the groove, the fixed seat and the rotary shaft are in matched connection through the boss and the groove, a groove is positioned on an excircle of the rotary shaft, bosses are respectively arranged in inner holes of the locking toothed plate and the fixed seat, the locking toothed plate is clamped in a clamp ring groove of the rotary shaft through a clamp ring to be fixed axially, and the unlocking handle is sleeved in an inner hole of a solid framework through a flange to be located axially. In locking, the angle adjusting device is in full-tooth mesh and is an infinite mode angle adjusting device. The angle adjusting device can lock at any angle and is simple in structure, large in locking moment and reliable in working. The angle adjusting device is not only used for adjusting chairs, but also used for adjusting angles of other articles, thereby being wide in application scope.