Lee Man-hee leads a church group with over 230,000 members.
Lee Man-hee, 88, heads the Shincheonji Church of Jesus. More than 5,000 of its members became infected, making up 36% of all Covid-19 cases in the country.
The authorities accuse him of hiding information about the group's members and gatherings from contact tracers.
The church says Mr Lee was concerned for his members' privacy, but never hid information from the authorities.
South Korea currently has 14,336 coronavirus cases, and 300 deaths.
Mr Lee was arrested early on Saturday, following an investigation. A judge said there were signs that evidence related to the case was being destroyed. Read more >>