(Updates to close)

By Kevin Buckland

TOKYO, May 28 (Reuters) - Japan's Nikkei share average

shed early gains of as much as 1.2% to end flat on Wednesday, as

the mood turned cautious ahead of earnings from artificial

intelligence chip leader Nvidia ( NVDA ) later in the day.

The Nikkei ended the day down 1.71 point at

37,722.40, effectively unchanged but snapping a three-day rally.

The broader Topix also finished essentially flat but up 0.02

point at 2,769.51.

Japanese stocks were initially buoyed by a sharply weaker

yen, which boosts the value of overseas revenues for the

country's many heavyweight exporters.

However, a poor auction of super-long Japanese government

bonds also saw yields pushing higher again, weighing on

sentiment.

The Nikkei particularly struggled above the key

psychological level of 38,000, after pushing as high as

38,178.73 in morning trading.

Some additional push is needed to take the Nikkei firmly

above 38,000, such as further positive developments in U.S.

tariff negotiations, said Masahiro Ichikawa, chief market

strategist at Sumitomo Mitsui DS Asset Management.

While a weaker yen supports sentiment, "one can't say the

foreign-exchange market has stabilized", he added.

Despite the more cautious finish to the session,

chip-testing equipment maker and Nvidia ( NVDA ) supplier Advantest ( ADTTF )

remained the Nikkei's biggest gainer in index-point

terms through to the close, ending with a 1.6% advance.

By contrast, chip-making machinery manufacturer Tokyo

Electron ( TOELF ) flipped from early gains to finish down 0.1%.

Automakers as a group had been strong in early trading but

ended the day mixed. Honda ( HMC ) climbed 1.3%, but Toyota ( TM )

reversed gains to drop 0.3%.

Nissan ( NSANF ) was among the most volatile stocks on the

day, leaping as much as 4.6% at the start of the afternoon

session following a media report that it plans more than $7

billion in fundraising to help turn the business around.

However, it shed those gains to end the day down 0.3%.