A device for injecting a viscous fluid into the body includes a tubular structure defining an inner bore for passage of the viscous fluid and a pushing piston (21) engaged in the inner bore. The tubular structure is a single-piece metal tubular body (3) extending from the first end (4) to a second end (5) provided with a connector (7) for sealable fastening of a trans-tissue injection vector. The pushing piston (21) has a metal rod (22) having a straight transverse section that is constant over its entire length and complementary, while allowing for operational clearance, with that of the bore of the metal tubular body (3).
