<p>On 21 November 1903, five Japanese were arrested in Bangkok on suspicion of counterfeiting Siamese (Thai) government notes. They were Iwamoto Chizuna, Yamamoto Yasutaro, Wada Inosuke (pseudonym of Sakutake Toranosuke), Sasaki Tokumo and Takahashi Sanya. These Japanese had just manufactured counterfeit banknotes in Japan and brought them to Bangkok on 10 November of the same year.</p><p>These Japanese were complicit in a banknote counterfeiting masterminded by two privileged Thais, one was Prince Pongsa (Kromma Muen Bongsa Disornmahip,1861–1936), half-brother of King Chulalongkorn, the other was Nai Peng Srisararaks (1867-?). The latter was the eldest son of Chao Phraya Phasakorawong and Lady Plian,who were most prestigious aristocrats in Siam.</p><p>The roles of the Japanese suspects were as follows: Yamamoto was a close friend of Nai Peng, and as a result, liaised with Iwamoto (written as Ewamoto in Thai documents), who was well known in Japan; Iwamoto used his network to find competent counterfeiting technician and Japanese funder; Sakutake was a counterfeiting technician; Sasaki was in Bangkok to liaise with the Thai mastermind; and Takahashi was a fund provider on the Japanese side.</p><p>Economic development in Thailand has resulted in the need to circulate paper money as well as silver coins. Thailand started using government banknotes on 23 September 1902, but within six months, the above two privileged Thais plotted to counterfeit banknotes and approached the Japanese to manufacture them.</p><p>It was not until 15 April 1903 that Japan’s first law (Imperial Ordinance No. 73) punishing the counterfeiting of foreign banknotes and coins etc. was implemented, and before that there was no law in Japan punishing the counterfeiting of foreign banknotes. Therefore, in February-March 1903, when Yamamoto, Iwamoto and other Japanese joined the counterfeiting of Siamese banknotes, the risk of being arrested for counterfeiting Siamese banknotes in Japan was low. In addition, Japan had extraterritorial jurisdiction rights in Thailand at the time, so Japanese nationals in Thailand were protected by the consular court, and even if they committed a crime in Thailand, Japanese law would be applied and they would not be punished under Thai law. Thus, counterfeiting Thai banknotes was a low risk for the Japanese, and they may have casually joined the conspiracy.</p><p>Iwamoto Chizuna, who had been living in Kyoto after contributing to the welcoming of Buddha relic from Thailand to Japan in June 1900, was complicit in the counterfeiting of Siamese banknotes.</p><p>This banknote counterfeiting case has been little known until now. This paper is the first to reveal the correct facts of the case by using official documents and newspaper reports from both Thai and Japanese sides.</p><p>At the same time, this paper reveals certain aspects of Thailand’s political and economic society at the beginning of the 20th century. For example, the efforts of the first Japanese minister to Thailand, Inagaki Manjoro, to build friendly relations with Thailand, economic activities of the Thai royal family and upper nobility, Japanese consular jurisdiction, the Thai judiciary not independent of the King, and Criminal penalties by the King for royalty who committed illegal acts.</p><p>(View PDF for the rest of the abstract.)</p>