Banknotes of Japanese yen are seen in this illustration picture taken September 23, 2022.
Bank of Japan Governor Haruhiko Kuroda also repeated his usual line that stability in the foreign exchange market was "extremely important", characterising the yen's recent softening as sharp and one-sided.
The comments came as the yen traded near a 32-year trough to the dollar at 149 yen, putting the major psychological barrier of 150 in focus.
"When looking at the global financial and economic environment surrounding Japan, downside risks are building up rapidly," Adachi said in the speech.
"When downside risks are so high, we should be cautious of shifting toward monetary tightening," he said, warning that heightening external headwinds risked tipping Japan back to deflation.