The 43-year-old man, originally from Bulgaria, called police after he found the weapons Sunday near Canal Saint-Martin in Paris, Radio France Internationale reported Thursday.
Police said they discovered a 6.35-caliber automatic pistol, four grenades, 16 rounds of ammunition and a mortal shell for an M-58 armored vehicle, all of which are used by the French army, in the trash can. The homeless man also told police that a wooden box filled with grenades found in the same area had been taken away in a dump truck.
"This was a completely inconsiderate act because the weapons were still operational and could have fallen into the wrong hands," an investigator told French radio RTL.
A bomb squad was called in to remove the weapons from the area.
Police said they identified the weapons as belonging to a collector who recently died. His family apparently decided to throw them out along with the collector's trash.