The entertainment and electronics giant dropped 1.67 percent to close at 996 yen as the benchmark Nikkei index lost 1.71 percent on the Tokyo Stock Exchange on Monday.
Dealers said Sony last traded below the psychologically important 1,000 yen level in August 1980 around a year after its landmark "Walkman" portable music player was released.
The total market value of the company is now around one trillion yen ($13 billion), compared with 11 trillion yen in 2000, there year the PlayStation was released and shares hit a peak of 16,950 yen, dealers and news reports said.
Sony posted a record full-year loss of 456.66 billion yen ($5.8 billion) for the year to March 2012 as it struggled with losses in its television division.
Japanese companies have blamed tough competition from rivals including South Korea's Samsung, falling prices, slow demand, the impact of severe flooding in Thailand last year, and the high yen for their travails.
The stronger yen hits Japanese exporters by making their products more expensive overseas, while eroding the value of foreign-earned profits.
Last month Sony said it would withdraw from a liquid crystal display joint venture with its domestic rival Sharp, which has announced an $808 million link-up with Taiwan's Hon Hai Precision.
In April, Sony said it would cut about 10,000 jobs and spend nearly $1 billion on an overhaul that its new chief executive Kazuo Hirai described as "urgent".
Sony has vowed it will swing back into the black as it embarks on the restructuring plan. The firm now forecasts a net profit of 30 billion yen in the current fiscal year to March 2013 on sales of 7.4 trillion yen.