The demonstration came hours after a delegation from the 15-nation regional bloc led by former Nigerian leader Abdulsalami Abubakar arrived overnight to press for a peaceful restoration of civilian rule.
"The army loves the people and will always stand beside Niger," leading junta member, Col. Djibril Adamou Harouna told thousands of demonstrators cramming streets surrounding a Niamey roundabout. "We wanted to come here today to thank you for your support."
On Thursday, the army turned on President Mamadou Tandja, raking the presidential palace with gunfire and whisking the ousted leader to a military barracks outside the capital. The soldiers swiftly announced a coup and said it was being led by Salou Djibo, a little known commander of a platoon just outside the city.
The junta has vowed to turn Niger into "an example of democracy" after Tandja stayed in office past his legal mandate, which expired in December. But the country's new rulers have not said how long they will hold power and some worry the move could increase the uranium-rich country's isolation.
Residents, at least those in the capital, appeared to overwhelmingly support the military action.
Tandja had grown deeply unpopular here after pushing through a referendum in August that established a new constitution which removed presidential term limits. It also gave him greatly boosted powers and an unprecedented three-year extension of his rule before another round of elections could be held.
Before the referendum, Tandja had been criticized for imposing rule by decree and dissolving parliament and the constitutional court because they opposed his plan to stay in power past his legal Dec. 22 mandate.
"We're proud of our military!" screamed one woman at Saturday's rally, where demonstrators held up hastily made signs scrawled with the words: "Long Live the Army."
"Tandja let everything go," said Amadou Madi, a 27-year-old electrician. "He was a thief and a crook. Our military was right to remove him."
Tandja first rose to power in democratic elections in 1999 that were organized by a military junta which took control that year. Many of the military masterminds responsible for organizing that ballot also took part in Thursday's coup, apparently disillusioned with Tandja's refusal to step down.
Tandja's attempt to stay in power prompted the 15-nation Economic Community of West African States, known as ECOWAS, to suspend Niger from its ranks, and the U.S. and Europe cut off aid to the uranium-rich nation. Resumption of aid is likely dependent on the nation holding new elections.