A parliamentary panel approved a long-awaited bill, effectively meaning it is guaranteed to become law, possibly as soon as Wednesday.
Analysts CSLA says Japan's casino market could be worth $40bn a year.
Las Vegas Sands shares closed 3% higher, while Wynn Resorts and MGM Resorts both added 2%.
Casinos are currently illegal in Japan, though gambling on horse, boat and bicycle races is allowed through government-backed bookmakers.
And the prospect of the country becoming a gambling powerhouse has excited operators who are keen to find new markets, especially those in close proximity to China.
The new bill, which will now go before politicians in Japan's upper house,  proposes allowing large-scale projects that will combine casinos with hotel, shopping and conference facilities.
Attracting tourists is one of the key economic policies of Japan's Prime Minister Shinzo Abe and supporters say these developments will bolster the country's flagging economy and help support  tourism after the 2020 Tokyo Olympics.
But there has been strong opposition based largely around fears of gambling addiction and other social fall-out such as organised crime.
And an opinion poll by public broadcaster NHK found 44% of those questioned opposed the plans, with just 12% supporting it and 34% of respondents undecided.
The most common form of gambling in Japan is Pachinko, the country's take on pinball. Played in parlours  across Japanese towns and cities, the game is tolerated despite its legal status remaining vague.
However even if the bill is passed, it will not be an immediate green light to open casinos. Instead it will allow regulators to begin developing plans on how to license the industry.
Shares in some of the world's biggest gambling firms have rallied after the legalisation of casinos in Japan moved a step closer.