The investment will make cash-bleeding Sony the single biggest shareholder in Olympus, with slightly more than 11 percent of its outstanding stock.
The companies will also establish a joint venture to develop endoscopes, with the focus on a type used in keyhole surgery, the statements said.
“At Sony we are aggressively pursuing the growth of our medical business, with the aim of developing it into a key pillar of our overall business portfolio,” said Sony president Kazuo Hirai in a statement.
“The business and capital alliances we have agreed with Olympus today will be integral to these plans,” he said.
Sony will take a 50 billion yen private placement of Olympus shares by the fiscal year-end for 1,454 yen a share.
The price represents a saving on Olympus’s shares on the open market, where they closed on the Tokyo Stock Exchange at 1,520 yen.
Olympus’s reputation was badly damaged after its British former chief executive blew the whistle last year on an accounting scam that saw $1.7 billion worth of losses moved off its balance sheet.
The camera-maker has since announced a major overhaul that includes cutting about seven percent of its workforce, while its new boss had publicly said he was seeking a capital injection to shore up the company’s finances.
Olympus reported a 4.46 billion yen loss in the April to June quarter.
For the fiscal year to March, Olympus has said it expects to book a net profit of 7.0 billion yen on sales of 920 billion yen.
“Investment from Sony will help strengthen our financial base,” said Hiroyuki Sasa, president of Olympus, in its statement.
The alliance will enable the embattled company to “contribute to world medical progress by developing a variety of new medical devices that would not be possible by Olympus alone”, he said.
For Sony, which continues to lose money in its mainstay television business, strengthening its medical equipment business has been a stated management goal.
The once-world-beating maker of the Walkman lost a whopping 456.66 billion yen in the year to March, its fourth consecutive annual loss.
It also reported a widening loss in its latest quarter and cut a profit forecast for the year.
Earlier this week ratings agency Standard & Poor’s downgraded its long-term corporate credit ratings on the firm to BBB, just two notches above junk status.