Kim Sang-ho, 70, together with four other South Koreans, stole the statue and 360 volumes of Buddhist scripture, worth around 110 million yen (USD 884,000) in total, according to the ruling by the Nagasaki District Court.
They were stolen in November last year from a temple on Tsushima island, about 50 kilometres (30 miles) from the Korean peninsula, which is dotted with temples and other relics that underline centuries of interaction.
The copper statuette, which stands about 10 centimetres (four inches) tall, was reportedly a ninth-century gift from the Korean kingdom.
The situation of the remaining four South Koreans involved in the theft is unclear.
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The island saw two ancient Buddha statues stolen in 2012 by Korean thieves.
Four people were arrested in South Korea in 2013 over that theft, after they tried to sell the statues which were then confiscated by the authorities.
Japan requested the two statues' swift return, but a South Korean District Court blocked their repatriation on suspicion that they might have been stolen from Korea centuries ago by Japanese pirates.