TOKYO (Reuters) - SoftBank Group Corp 9984.T said on Monday it was considering listing its Japanese wireless business - a move that could reportedly raise $18 billion and would accelerate the conglomerate's transformation into one of the world's biggest tech investors.

A spin-off - potentially the biggest IPO by a Japanese company in nearly two decades - would give the unit more autonomy and help investors value the business as well as its parent which has myriad holdings across the tech industry.

SoftBank Group is aiming to sell about 30 percent of SoftBank Corp, Japan’s No. 3 wireless carrier, for around 2 trillion yen ($18 billion), the Nikkei newspaper said without citing sources. It added that proceeds will go towards investments in growth such as buying into foreign information technology companies.

“It makes sense to spin off the mobile-phone business using a public offering that would leave SoftBank in control and provide SoftBank with more cash to pursue its strategy of investing in companies with potentially high growth prospects,” Erik Gordon, a professor at the University of Michigan’s Ross School of Business.

“It is a way of obtaining capital without adding debt or diluting SoftBank’s equity interests in the growth companies.”

SoftBank Group plans to seek approval from the Tokyo Stock Exchange as early as spring, the Nikkei said, adding that it was aiming to list around autumn in Tokyo as well as overseas, possibly London.

The conglomerate said in a statement that a listing of the telecoms business was one option for its capital strategy but that no such decision had been made. Its shares finished 3 percent higher on the news.

An IPO of about 2 trillion yen would be one of the biggest offerings by a Japanese company, rivaling a 2.1 trillion yen listing by NTT DoCoMo Inc 9437.T in 1998 and the 2.2 trillion yen raised by the government's sale of Nippon Telegraph and Telephone Corp 9432.T shares before its 1987 listing.

Large companies seeking to list in Tokyo are required to float at least 35 percent of their shares although these rules can be eased when the company is also listing overseas.

FILE PHOTO: The logo of SoftBank Group Corp is displayed at SoftBank World 2017 conference in Tokyo, Japan, July 20, 2017. REUTERS/Issei Kato/File Photo

COMPLEX STRUCTURE

SoftBank Group has a vast range of holdings including stakes in British chip designer ARM Holdings ARM.L, struggling U.S. wireless service provider Sprint Corp S.N as well as Alibaba Group Holding Ltd BABA.N.

It has with other investors also set up a $93 billion Vision Fund that is investing in a range of firms to capitalize on a tech future expected to be driven by artificial intelligence, robotics and interconnected devices.

That complicated structure and constant stream of new investments has made valuing the company extremely difficult and analysts often note that its market value does not accurately reflect the value of its massive holdings.

SoftBank Group’s market capitalization currently stands at around $92 billion. By contrast, its near 30 percent stake in Alibaba is worth around $140 billion.

An IPO could lead to softness in SoftBank Group shares for a while as some telecoms-focused investors sell their holdings to buy shares in the newly listed entity, said Chris Lane, an analyst at Sanford C. Bernstein.

“What SoftBank will ultimately have to do, and they would have to do this in any case, is attract investors who are looking at this as a tech focused investment co(mpany),” he said.

The domestic telecoms unit posted a 4.5 percent rise in operating profit to 720 billion yen in the year ended March on sales of 3.2 trillion yen.

While it has been SoftBank Group's most profitable source of income, it faces headwinds including an aging population, a shift by consumers to cheaper carriers and plans by e-commerce firm Rakuten Inc 4755.T to enter the market.

With SoftBank’s founder Masayoshi Son reluctant to sell stakes in investments seen as having large upside potential such as Alibaba, listing the telecoms business could provide a place to park some of the conglomerate’s large debt burden.

“If the desire is to be able to raise capital for future vision funds, pushing as much of the debt into the telco as possible makes sense,” said Lane.

SoftBank’s debt pile stood at around $100 billion in the financial quarter ended September.