Police had just sealed off the area after a postman spotted the bomb outside the Maison Blanche Metro station - the same name as that of the village where gendarmes shot dead Algerian-born Khaled Kelkal a week ago.
"The toll would have been much worse if the alert hadn't been given," police said. The 2.5kg (5.5lb) bomb was a gas canister filled with nails and bolts. The technique was used by Muslim fundamentalists in previous attacks.
Most of the injured, who included a child and two policemen, suffered ear trouble from the blast. Nine were taken to hospital but all were released after a few hours. An anonymous caller to France's RTL radio claimed the Algerian militant Armed Islamic Group (GIA) carried out the bombing.