Speaking after a three-day visit, Yasushi Akashi said Japan and Norway would play a complementary role in facilitating the peace process.
He said he will travel to other countries, including the United States and India, in a bid to attract donations to help rebuild Sri Lanka.
The former UN diplomat said the peace process in Sri Lanka was progressing well.
Mr Akashi said he was initiating a study to identify the needs of the entire country before Tokyo arranges a conference for international aid donors in June.
The Colombo government and the rebel Liberation Tigers of Tamil Eelam have been observing a Norwegian-brokered truce since February last year and have held four rounds of formal peace talks.
More talks will be held in Thailand next month, before a sixth round in Japan in March.
- Australian Broadcasting Corporation
- © ABC