At 9:15am on Monday the OMXS index had risen 0.6 percent to 413.83. The previous record, set on March 6th 2000, was 413.72.
The stock market boom in 2000 was followed by two years of falls. The market reached its nadir in October 2002 at 126.4. Since then, it has risen by 225 percent.
Share analyst Peter Malmqvist of Nordnet said he was surprised that the record had been broken.
“I’m surprised that we are reaching a new all-time high now, given the question marks over US growth and given that inflation and interest rates are on the up,” he said.
Malmqvist said that the record could itself have a positive psychological effect.
“A record often attracts money – it’s attractive to follow a positive trend, at least in the short term,” he said.
Among the winners on Monday were clothing chain H&M, which released positive sales figures on Monday. The company’s share price rose 2.8 percent.
Telecoms equipment maker Ericsson and engineering company Atlas Copco both rose 1.0 percent. Sandvik was up 0.8 percent and steel company SSAB was up 2.2 percent.
Just before 10am the index had fallen back below the record level, down to 413.24.