Tank (11) for a drug infusion device (41), comprising a hollow cylindrical body (13) provided at its front with an opening (15) for the passage of the drug and in its inside with a plunger (25) slidable within the tank for drawing in and/or injecting the drug through said opening, said tank being provided at its rear with a coupling part for ensuring the mechanical connection of the tank (11) with a complementary coupling part provided in the infusion device (41), said coupling parts defining together a bayonet-like connection coupling, said coupling part of the tank (11) being housed inside the cylindrical body (13).
