The stock market has stayed the course in making gains, and the benchmark Nikkei 225 average finished at 19,254.25 on Friday, its highest level in 15 years, and top government officials were quick to give credit to “Abenomics” economic and financial policies, claiming they have been a boon for market participants.

But skepticism has remained strong among analysts and traders. All market participants know that the Tokyo Stock Exchange has, more or less, been propped up by massive buying out of public funds, including those from Japan’s public pension funds and the Bank of Japan.

The Government Pension Investment Fund (GPIF), the world’s largest institutional investor, is often compared to a “whale” in the Tokyo stock market given its massive assets — estimated at around ¥130 trillion.

Under the initiative of Prime Minister Shinzo Abe’s Cabinet, the GPIF announced in October a change in its investment policy.

GPIF is now trying to raise the ratio of domestic stocks in its basic portfolio to 25 percent from the 12 percent with a margin of plus or minus 9 percentage points — a huge benefit for stock traders.

According to an estimate in the March 6 report by Tomohiro Okawa, a strategist at UBS Securities Japan Co., the potential inflow from public institutions and pension funds into Japan’s stock market could be as high as ¥27.2 trillion.

Those public funds include GPIF, “Kampo” postal insurance, Japan Post, the Bank of Japan and other pension funds.

GPIF has said it has changed its investment policy to adapt to the changing economic environment, and thereby gain higher returns for pensioners.

But many are concerned the current stock prices may have been bloated by massive buying by GPIF and other public funds, though the government has consistently denied any market manipulation to boost stock prices.

“Public funds now start buying stocks when prices fall. I don’t think they have bought at close to peak prices, but it’s true they have greatly reduced downward risks,” said Tomoichiro Kubota, a senior market analyst at Matsui Securities Co.

Now, economic indicators of the domestic economy are not enough to boost the Nikkei above 19,000, Kubota argued.

“If (public funds) like GPIF and the Bank of Japan stop buying stocks, (the Nikkei) wouldn’t have reached 19,000,” he said.

Kubota believes GPIF still has plenty of room to keep buying domestic stocks before the ratio reaches the portfolio target of 25 percent, thus there is little risk for investors — at least for the time being.

“But if you think of a long-term period of, say, five or 10 years, yes, there should be some risk,” he said.

During a Lower House session on Thursday, Goshi Hosono, policy chief of the Democratic Party of Japan, pointed out that selling by individuals outnumbered buying by ¥3.8 trillion on the first section of the Tokyo Stock Exchange in 2014, while trust banks bought a net ¥2.76 trillion the same year. Hosono claimed most of the funds of trust banks came from the GPIF.

“Why are stock prices rising? Trust banks are buying far more stocks than they sell, which has pushed up prices,” Hosono said.

“This condition of the stock market is rather unsound,” he added.

During a news conference on Friday, Chief Cabinet Secretary Yoshihide Suga said the government will not comment on the volatility of stock prices because it could “unnecessarily upset the market.”

But at the same time, he claimed market participants “should have analyzed the (Japanese) economy” by giving consideration to various government measures to pull the economy out of deflation.

Nobuhiko Kuramochi, head of investment department of Mizuho Securities Co., does not believe the GPIF has changed its investment policies to artificially boost stock prices.

It is true that the GPIF’s reform had a positive impact on the overall stock market, but that alone would not be enough to create the recent rising spree on the Tokyo Stock Exchange, Kuramochi argued.

According to the latest Tokyo Stock Exchange figures, foreign investors — another key TSE player — bought a net ¥176.4 billion worth of stocks in February and ¥210 billion worth in the first week of March.