(1)Aim (Introduction). There are far more studies of English, French and German urban history than those of Scandinavian in Japan. The aim of this article is to produce the subject matter in behalf of the discussion on mediaeval urban history of Europe by means of showing the investigative result of Bjarkeyjar rettr applied to Nidaros (Trondhjem), which was compiled in the 12th and 13th centuries. (2)Relation to Frostupingslog [ch. 1, (1)]. The document describes Nidaros as 'kaupang' and its law effective area as 'takamarki' (§173). The area covering Nidaros is geographically called 'herao' which stands under the jurisdiction of Frostupingsrettr. Inquiring into the law relation of these two areas (§§2, 43, 102), the author can not find no superiority or inferiority between them (cf., Frostupingslog §X-32, K.M.Haakonssφns Landslov §V-16, K.M.Haakonssφns Bylov §V-16.). (3)Meetings [ch. 1, (2)]. Moots (mot) are held by the chief executive officer (gjaldkeri) and the house-holders (husfastir menn) who stay over three months (e.g., §§6, 14, 18, 24, 25, 26, 34, 44, 47, 52, 108, 135, 173). In addition the law-assembly (logping) (§9) and the weapon-assembly (vapnaping) (§137) are also held. The latter is based on the residents' duty of self-defence against the enemy invading Nidaros (§25). Assemblies (ping) are also held in many cases (§§72, 98b, 144, 145, 157, 158, 163). Administration in general is thus performed, and they enjoy the autonomy. The residents are classified in some strata between the slave (praell) and the superior yeoman (hauldrmaor) (§§47, 127, 140, 142, 145, 162) [ch. 2, (1)]. (4)Character [ch. 2, (2) (3)]. The citizen is described as 'boejarmenn', and the word 'bondi' is also used as its synonym. It can be surmised that 'bondi' are engaged not only in agriculture and cattle-raising, but also in forestry, fishery and hunting (seals) (§§60, 63, 138, 144, 146, 158). It can therefore be judged that Nidaros has agricultural, fishing, and so forth characters. She also has a character as a commercial and port town (§§4, 6, 7, 107, 108, 153-4, 168-77). (5)Social background [ch. 3, (1) (2)]. Outlawry is condemned in many cases (e.g. belief in paganism) (§§2, 10, 12, 14, 33-5, 46, 51, 65, 69, 118, 128, 131, 152), but in fact it can be atoned without punishment in many cases (§§72, 101. cf., §§147, 168. exception : §§13, 18, 28, 50). Thefts concerning agriculture, cattle-raising and so on meant violations of private ownership (§§112, 118-9, 147-8). Land (land, joro) is indeed under private ownership, but 'eign' (§§63, 146) is under possession, or holding. Land (eign) is intended to be transformed under private ownership (land, joro) on one hand, but the aim is also regulated on the other hand, and of the promotion and the regulation stand side by side. (6)Conclusion. Nidaros is an autonomous community with a complex (agricultural, fishing, cattle-raising, commercial) character, and also a mediaeval society preserving ancient features.