The company sold 300,000 of the Wi-Fi-only iPads in its first day of availability in the US, including pre-orders.
"One million iPads in 28 days - that's less than half of the 74 days it took to achieve this milestone with iPhone," said Apple CEO Steve Jobs.
"Demand continues to exceed supply and we're working hard to get this magical product into the hands of even more customers."
Due to the high demand, Apple revealed last month it was pushing back the UK launch date of the iPad. The device will be made available for pre-order on May 10, with iPads to be released at the end of the month.
The original iPhone may be a good barometer for the iPad's success, though it's worth noting that subsequent versions such as the iPhone 3G and the iPhone 3GS each hit the same milestone in their first weekend.
But the iPad, even more so than the iPhone, is a device in an unproven, entirely novel category, which makes the accomplishment all the more impressive.
Plus, the iPad sales bring with it sales of additional products: iPad users have already downloaded more than 12 million applications and more than 1.5 million e-books from the iBookstore.
And the number of iPad-specific apps continues to rise, with Apple's latest figure topping 5,000.
If nothing else, one million sales would seem to validate the iPad as a product.
We'll have to wait until Apple's next quarterly results in July to see how it plays out for the company's bottom line, but until then, have no fear: analysts will no doubt fill that vacuum with endless amounts of speculation.
See also: 12 ways to improve the Apple iPad