An orthodontic appliance that by ensuring proper occlusal position of teeth in an oral cavity enables teeth straightening to thereby achieve precise correction ensuring proper occlusion and enables performance of teeth straightening by residing in the oral cavity for a certain time period such as during sleep. A configuration includes an orthodontic unit to be removably fitted in the oral cavity and molar caps erected near the orthodontic device. The orthodontic unit includes a pair of U-shaped devices formed of a maxillary orthodontic unit and a mandibular orthodontic unit united by wires. Teeth are straightened while adjusting positions of upper and lower jaws. The molar caps include large covering lids for anchoring that are slightly higher than surrounding teeth. The orthodontic unit is mounted on outer peripheries of the molar caps by locking to the molar caps through grooves provided in the maxillary orthodontic unit of the orthodontic unit.
