An automatic drug injection device comprising - an outer body (1; 100) extending along a longitudinal axis, - a syringe group (6; 106) placed in said outer body (1; 100) and fixed thereto, said syringe group comprising a syringe (7; 107) containing a drug to be injected, a needle (7a; 107a) and plunger means (8; 108) axially slidable and pivotable relative to said outer body (1; 100), - means for arming (4; 104, 204) said device from a stored position to a first armed position for injecting a first dose and at least a second armed position for injecting a second dose, said arming means being arranged at one end of the outer body (1; 100), - first elastic means (10; 110) arranged between said arming means (4; 104, 204) and said plunger means (8; 108), said first elastic means being in compressed condition when the device is in its stored position and decompressing to push forward said plunger means (8; 108) and deliver successively said first and said at least second dose, - a sliding sheath (30; 130) arranged at the other end of said outer body (1; 100) and constrained to slide axially thereinto, as a result of a pressure exerted on its free end, in contrast with second elastic means (35; 135) arranged between said sliding sheath (30; 130) and said outer body (1; 100), between a sliding lock-out position, in which said sliding sheath (30; 130) projects from said outer body (1; 100) covering the needle (7a; 107a) of the syringe, and a device trigger position, in which said sliding sheath (30; 130) is retracted in said outer body (1; 100) leaving the needle (7a; 107a) of the syringe exposed, said second elastic means (35; 135) being suitable to bring said sliding sheath (30; 130) back to said lock-out position when said pressure action ceases, - drive cam means (28; 128) operatively connected to said sliding sheath (30; 130) and axially pivotable in said outer body (1; 100), - trigger cam means (26, 27; 126, 127) pivotable integrally with said drive cam means and connected operatively with said plunger means (8; 108) to angularly displace said plunger means (8; 108) to said trigger positions of the first dose and the at least second dose, - stepped guide means (44; 144) integral to said outer body (1; 100) and operatively connected with said plunger means (8; 108) to control the extent of the axial sliding of said plunger means (8; 108) and therefore limit the volume of drug delivered for each dose, said trigger cam means (26, 27; 126, 127) and said drive cam means (28; 128) being formed on a same support (23; 123) pivotally arranged between said outer body (1; 100) and said plunger means (8; 108). - an outer body (1; 100) extending along a longitudinal axis, - a syringe group (6; 106) placed in said outer body (1; 100) and fixed thereto, said syringe group comprising a syringe (7; 107) containing a drug to be injected, a needle (7a; 107a) and plunger means (8; 108) axially slidable and pivotable relative to said outer body (1; 100), - means for arming (4; 104, 204) said device from a stored position to a first armed position for injecting a first dose and at least a second armed position for injecting a second dose, said arming means being arranged at one end of the outer body (1; 100), - first elastic means (10; 110) arranged between said arming means (4; 104, 204) and said plunger means (8; 108), said first elastic means being in compressed condition when the device is in its stored position and decompressing to push forward said plunger means (8; 108) and deliver successively said first and said at least second dose, - a sliding sheath (30; 130) arranged at the other end of said outer body (1; 100) and constrained to slide axially thereinto, as a result of a pressure exerted on its free end, in contrast with second elastic means (35; 135) arranged between said sliding sheath (30; 130) and said outer body (1; 100), between a sliding lock-out position, in which said sliding sheath (30; 130) projects from said outer body (1; 100) covering the needle (7a; 107a) of the syringe, and a device trigger position, in which said sliding sheath (30; 130) is retracted in said outer body (1; 100) leaving the needle (7a; 107a) of the syringe exposed, said second elastic means (35; 135) being suitable to bring said sliding sheath (30; 130) back to said lock-out position when said pressure action ceases, - drive cam means (28; 128) operatively connected to said sliding sheath (30; 130) and axially pivotable in said outer body (1; 100), - trigger cam means (26, 27; 126, 127) pivotable integrally with said drive cam means and connected operatively with said plunger means (8; 108) to angularly displace said plunger means (8; 108) to said trigger positions of the first dose and the at least second dose, - stepped guide means (44; 144) integral to said outer body (1; 100) and operatively connected with said plunger means (8; 108) to control the extent of the axial sliding of said plunger means (8; 108) and therefore limit the volume of drug delivered for each dose, said trigger cam means (26, 27; 126, 127) and said drive cam means (28; 128) being formed on a same support (23; 123) pivotally arranged between said outer body (1; 100) and said plunger means (8; 108).