Japan's Defence Minister Shinjiro Koizumi accused China of rapidly increasing military capabilities without transparency.
Speaking at the Shangri-La Dialogue in Singapore, he said China's defence spending continues to rise at a high level, causing serious concern.
Koizumi refuted allegations of 'new militarism', noting Japan has no nuclear weapons or strategic bombers.
He stressed Japan has consistently respected international law since WWII and seeks dialogue for regional stability.
Koizumi expressed sadness at not meeting his Chinese counterpart at the forum.
In April, Tokyo announced its biggest overhaul of defence export rules in decades.
