The theory of the ‘Threefold Circle-Body’ (三輪身) refers to the three kinds of buddhakaya: ‘xixing-lun-shen’ (自性輪身) denotes the tathagata; ‘zhengfa-lun-shen’ (正法輪身) denotes the bodhisattva; and ‘jiaoling-lun-shen’ (教令輪身) denotes the vidyaraja. Of these, zhengfa-lun-shen and jiaoling-lun-shen are described in the Prajñaparamitanayasatapañcasatika (般若理趣釈) and the Renwang-niansong-yigui (仁王念誦儀軌), both of which were translated by Amoghavajra (不空); xizing-lun-shen can be found in the She-wuai jing (摂無礙経). Although the ‘Threefold Circle-Body’ theory was developed in Japan, it is thought to have not yet been properly formulated until the time of Kakuban (覚〓). However, Annen (安然), who established Tendai esoteric Buddhism (台密) in Japan, uses the term ‘Twofold Circle-Body,’ (二種輪身) in connection with the tathagata, as well as referring to the ‘Threefold Circle,’ in his major work, the Bodaishingi sho (菩提心義抄). Until now, it has been supposed that the ‘Threefold Circle-Body’ had not yet been developed by the time of Annen, as it has been assumed that the ‘Three-Circle’ model described by Annen is unrelated to the ‘Threefold Circle-Body’. In this paper, however, it will be argued that Annen's model is indeed greatly related to the formation of the theory of the ‘Threefold Circle-Body’. To this end, we shall take into consideration the relation between the tathagata, bodhisattva and vidyaraja in Annen's theory of buddhakaya, as well as its influence upon later thinkers.