The Nikkei 225 included 0.3%, or 57.7 focuses, to end at 20,881.2.
It was the best complete for the file since 1996 and takes after new record highs on Wall Street overnight.
A fortifying Japanese economy, strong corporate outcomes and perky mind-set on US markets have helped goad picks up.
The Nikkei has bounced back from underneath the 15,000 level hit in June a year ago after the Brexit vote shook certainty on worldwide markets.
Speculators have furrowed once again into shares following the decision of US President Donald Trump, and his enormous spending designs and the guarantee of tax breaks. The three noteworthy US indicies - the Dow, Nasdaq and S&P 500 - achieved new highs on Tuesday.
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For Japan, more picks up could be in locate with solid corporate benefits expected amid comes about season this month.
The world's third-biggest economy has been grabbing steam, indenting its longest string of quarterly picks up in 10 years.
Japan has profited from rising fares - including advanced mobile phones and memory chips - while speculation fixing to the Tokyo 2020 Olympics has likewise given its economy a lift.
On Tuesday, the International Monetary Fund raised its worldwide financial viewpoint for Japan. It now expects 1.5% GDP development in 2017, and 0.7% the next year following an ascent in fares and shopper spending.
That is up from prior projections for 1.3% and 0.6% individually.
In spite of rupturing a two-decade high, not all stocks fared well in Japan on Wednesday.
One of the nation's biggest steelmakers, Kobe Steel, dove once more, with shares tumbling 36% of every two days in the wake of an embarrassment over the manufacture of information concerning the nature of its items.