The former Suntory chairman Takeshi Niinami, who resigned this week over allegations that he bought a supplement that could be illegal in Japan, has declared his innocence, saying he used the product to cope with jet lag and had never taken it within Japan’s borders.

At a news conference in Tokyo on Wednesday, Mr. Niinami said he had purchased supplements containing CBD, a cannabis compound commonly used for pain and anxiety, in the United States, where they are legal. The authorities are looking into whether the supplements are illegal in Japan, but Mr. Niinami said that because he never possessed them in the country, “I believe I did not violate any laws and am innocent.”

An influential executive, Mr. Niinami, 66, has traveled the world on business trips for many years, and he has continued to do so since becoming chairman of Suntory, the Japanese beverage giant, in March, after serving a decade as chief executive.

“It was my carelessness that led to this situation when I purchased these supplements,” Mr. Niinami said. “I apologize for the uproar it has caused.” He added, “I travel a lot for work and often suffer from jet lag, so an acquaintance who helps me stay healthy recommended it to me.”

Mr. Niinami resigned from Suntory this week after the authorities searched his home in Tokyo on suspicion that he had violated the Narcotics Control Law. The company’s board of directors said he had demonstrated “a lack of awareness” that rendered him “unable to continue in the key position of representative director and chairman.”

Mr. Niinami, who is also the chairman of Japan’s Keizai Doyukai business lobbying group, said he hoped to continue in that role. The Keizai Doyukai is assembling an ethics review committee to decide its stance on the matter.