City officials said the man, one of six construction workers who were missing after Tuesday's collapse, was taken to a hospital where he was pronounced dead.
Dozens of rescue workers assisted by dogs, drones and heavy equipment have been deployed in the search, but their efforts have been slowed by concerns about the stability of the apartment building in the city's Hwajeongdong district.
About 10 vehicles were destroyed and the occupants of nearly 200 nearby houses and shops were forced to evacuate following the collapse, which sent debris spilling across nearby streets and left a huge pile of broken concrete at the bottom of the structure, exposing mangled steel beams.
The incident has triggered public anger in a country that has long grappled with deadly accidents attributed to lax safety standards and regulations, which experts say were often overlooked during South Korea's rapid economic growth.
Police and officials from the Ministry of Employment and Labour on Friday raided a local office of HDC Hyundai Development, the main contractor for the project, as part of an investigation into whether the company violated safety laws.
Some experts have speculated that not enough time was allowed for the concrete to fully dry and set during the cold and snowy weather.
HDC issued a statement saying it "deeply apologises to the people who are missing, their families and the citizens of Gwangju," but did not comment specifically on what caused the collapse.
The Gwangju government has suspended all five of HDC's ongoing construction projects in the city and said it could force the company to tear down the damaged building and rebuild it from scratch if the structure's safety isn't assured.
Officials said 394 workers were employed at the Hwajeongdong construction site, including the five who are still missing. Emergency workers rescued three labourers on Tuesday, including two who had been trapped in a shipping container hit by debris, but search operations were halted hours later over concerns that the structure could collapse further.
