The An Yong-bok incident occurred in the spring of 1693 when Korean fishermen from Busan and Ulsan clashed with other fisherman from Otani and Murakawa at Ulleung-do.
An Yong-bok and Pak Eo-dun (박어둔) were captured and taken to the Yonago in the Tottri clan (modern-day Yonago city and Tottori Prefecture).
The pair was detained at a house in Yonago for two months, while this case was investigated by the Tottori clan. The shogunate ordered his subjects to send them to the magistrate at Nagasaki, an area controlled by the Tsushima clan. An Yong-bok was held hostage by the lord of Tsushima clan (So Yoshitsugu) again. When An Yong-bok was repatriated to Korea, the Tokugawa Shogunate demanded the prohibition of Koreans going to Ulleung-do. This led to diplomatic friction between Japan and Korea.
After An Yong-bok was repatriated to Korea, he testified that "the Kanpaku (Imperial regent) of the Tokugawa Shogunate made a note that confirmed Ulleungdo as Korean territory and he was in possession of the note until he was seized en route to Korea by the lord of Nagasaki, upon which the note was confiscated and he was held on the grounds of trespassing onto Japanese territory."
Korean scholars consider this testimony a fact. Japanese scholars, however, insist that this testimony is primarily Ahn's claim without supporting evidence because he did not go to Edo, the capitol of the Shogunate, and the Shogunate demanded Koreans be prohibited from going to Ulleung-do.
As a result of diplomatic negotiation; in January 1696 a senior statesmen of the shogunate issued the following instructions to the lord of Tsuhima clan (translated into English):
- Ulleungdo is about 160-ri (640 km) from Oki, but only about 40-ri (160 km) from Korea; therefore, it can be considered that Ulleungdo is the same as Takeshima and is an island belonging to Korea.
- Japanese are forbidden henceforth to make passage to Takeshima for the Japan-Korea friendship because the island is useless.
- The lord of Tsushima should communicate this to Korea.
Though the Tottori clan reported to the shogunate that "Takeshima does not belong to Inaba state (因幡) nor Hoki state (伯耆). There are no other islands belonging to the two states including Takeshima (Ulleungdo) and Matsushima (Liancourt Rocks)," the shogunate did not order a prohibition of Japanese going to Matsushima (Liancourt Rocks). In the diplomatic negotiation between Japan (Tsushima clan) and the Chosun government, they never discussed the Liancourt Rocks.
In 1696, Ahn visited Japan again. According to a Japanese record found in May 2005, the Bafuku is the investigation on An Yong-bok who arrived in Hokishu in May 1696 via the Oki Islands. The document has a total of 15 pages. The fifth page records Anyongbok's statement that Jasando (Usando) is Matsushima (松島) The last page records the eight provinces of Korea. The document specifically states that Takeshima (竹島 Ulleungdo) and Matsushima (松島 Liancourt Rocks) are part of the Gangwon Province (江原道).
The principal retainer of the Shogunate directed the Tottori clan to send him away because only the Tsushima clan has the right to determine matters of diplomacy with Joseon. According to the Sukjong Sillok, Ahn testified as follows after he was banished by the Tottori clan and returned to Joseon.
I sailed to Ulleung-do and the Usando again with the company of sixteen fishermen, disguised as a naval officer, and clashed again with the Japanese at Ulleung-do. The Japanese said they were living on Matsushima and strayed onto Ullungdo while fishing and would return. I fulminated at this, demanding to know why the Japanese were living on a Korean island. Upon arriving in Japan, I stated to the lord of the Tottori clan that "though it was confiscated by the Tsushima clan, I had held the Tokugawa Shogunate's edict that both islands were Korean possessions before visit. When I declared my intention to appeal to the Kanpaku, for the Shogunates edict to be upheld, the lord of Tsushima clan came to Tottori and entreated me to stop.