A syringe which can be correctly quantified includes a syringe, a cylinder body, a retaining edge and a cylinder hole； a push-pull piece, which can seal the cylinder hole of the syringe flexibly, has a rod body, and a plurality of inserting holes are arranged on the rod body longitudinally and spaced in the form of incompatible holes； a plurality of positioning pieces, each having a body, and a inserting hole column which can be inserted with a inserting hole of the corresponding shape and size of the pushing and pulling piece The body of the positioning piece can stop at the retaining edge of the needle cylinder.一種可正確定量的注射器，包含有一針筒，具有一筒身，一擋緣，一筒孔；一推拉件，可活動地密封該針筒的筒孔，具有一桿身，多個插位孔呈互不相容孔形縱向間隔地開設於該桿身；多個定位件，各具有一本體，一插孔柱可插設該推拉件對應形狀尺寸的一插位孔，該定位件的本體可擋止於該針筒的擋緣。
