Berkshire Hathaway Chairman Warren Buffett said stocks are cheap when measured against the current level of interest rates.
In an interview with CNBC on Monday, he added that stocks are not in bubble territory. If interest rates rise, however, they would make the market more expensive, he said.
He said he has invested about $US20 billion in stocks since shortly before the election.
Stocks extended their rally last week, with the Dow Jones Industrial Average closing at a record high for an 11th straight trading session, the longest streak since 1987.
Even before the post-election rise, several measures of valuation showed that stocks are about as expensive as they were during the tech bubble. Stocks were considered expensive because the median P/E ratio was well above its historical average, indicating higher prices than are justified by the underlying earnings-based value of the companies.
Buffett said he had raised his stake in Apple to 130 million shares, more than double the amount held as of December 31.