BOAO, China—The head of the International Monetary Fund praised Japan's latest massive monetary-easing program—one that has drawn criticism from China—as a "welcome step."

"Monetary policies including unconventional measures have helped prop up the advanced economies and in turn global growth," Christine Lagarde told the Boao Forum for Asia, a forum based in China that attracts business and government leaders from around Asia. "The reforms just announced by Bank of Japan are another welcome step in...