Japanese Prime Minister Shinzo Abe has arrived in Bangkok for a two-day visit and talks on Thursday evening with Prime Minister Yingluck Shinawatra.
Mr Abe flew to Thailand from Vietnam. He will leave on Friday for Indonesia, the last stop on his first overseas trip since being appointed prime minister.
The Japanese embassy said in a statement Mr Abe's trip is to enhance the partnership between Japan and the region, and to lay groundwork for the Japan-Asean commemorative summit in Tokyo in December.
The embassy statement said Thailand and Japan "share fundamental values and economic interests", and Japan considers Thailand as a hub of Japanese corporate activities.
Mr Abe has been granted an audience with His Majesty the King.
Ms Yingluck will host talks between Thai officials and the visiting Japanese on Thursday evening at Government House, a Thai government statement said.
The Thai Board of Investment (BoI) said Japan is the biggest overseas investor in Thailand. Between 1970 and 2012, Japanese investors applied for investment promotional privileges for 7,302 projects with a combined investment of 2.7 trillion baht - about one-fourth of all foreign investment in the country.
In Vietnam, Mr Abe committed Japan to a US$500 million assistance package to fund three Vietnamese development projects to be named later, the Vietnam News Agency reported.