TOKYO — A Japanese airline has apologized to a disabled rights activist, who is partly paralyzed, after it tried to prevent him from boarding a flight at a remote airport, prompting him to crawl up a portable boarding staircase to reach the plane’s cabin.

The airline, Vanilla Air, a budget affiliate of Japan’s largest carrier, All Nippon Airlines, said it offered the apology earlier this month in response to the incident, which occurred on June 3. The episode drew public attention this week — including outrage against the airline, but also criticism of the activist — after reports surfaced in the Japanese news media.

The activist, Hideto Kijima, said Vanilla Air staff initially told him he would not be allowed to board the small aircraft, which was flying from a small airport on the southern island of Amami to Mr. Kijima’s home in Osaka, because it lacked wheelchair-accessible boarding ramps or elevators.

Mr. Kijima was paralyzed from the waist down while playing rugby as a teenager and now uses a wheelchair.