Kishida took a PCR test “after experiencing a mild temperature and a cough” from Saturday evening, an official from the Prime Minister’s Office of Japan told AFP.
Reports in local media including public broadcaster NHK said he may now attend the August 27-28 Tokyo International Conference on African Development (TICAD) remotely.
Japan has logged record Covid-19 cases in recent days, although its total death toll from the disease is far lower than many other countries, at 36,780.
The 65-year-old Kishida, who took office in October, had his fourth vaccine shot earlier this month.
He has been on holiday with his family and was due to return to work on Monday.
Japan has never imposed a strict lockdown, and anti-infection measures mainly targeting bar and restaurant opening hours were lifted in March across the country.
The nation’s borders have partially reopened although tourists are still banned unless they are on organized group trips.
Tokyo has partnered with African countries since 1993 to hold TICAD around every five years.
At the upcoming meeting, Japan will strongly support “African-led development” with a focus on economy, society, and peace and stability, a Japanese foreign ministry briefing document said.
Japan would also contribute to enhancing food security in Africa to address the food crisis which had worsened due to the situation in Ukraine, the document said.
