Injection device for injecting liquid medication into a patient, comprising: - a housing (1), - a static structure (2) comprising a first gear element (14), said static structure (2) being in its fixed assembly with respect to the housing (1), - a dynamic structure (3) comprising a medicament container (11), means (6, 7, 8) for pushing liquid medicament out of said medicament container (11) for injection in a patient, and a second gear element (13) engaged with the first gear element (14), said dynamic structure (3) as a whole allowing movement with respect to the housing (1), - an element ( 4) drive to drive one of the first (14) and second (13) gear elements to cause the dynamic structure (3) to move relative to the static structure (2) along one direction (D) predetermined due to the engagement between the pri gear elements mere (14) and second (13), and - clutch means (23, 25, 28) to keep the gear between the first (14) and second (13) gear elements in normal condition of the injection device, and for allow the first (14) and second (13) gear elements to be disengaged when the injection device receives a shock along the predetermined direction (D), said clutch means comprising: - means (23) to allow that the other of the first (14) and second (13) gear elements move away from said one of the first (14) and second (13) gear elements and in this way one of the gear elements is disengaged from said first (14) and second (13), - a blocking element (25), which, in a predetermined position, prevents the other of the first (14) and second (13) gear elements from moving away from said one of the first (14) and second (13) gear elements, and - a recovery spring (28) for maintaining er to the locking element (25) in the predetermined position, the force of said recovery spring (28) being overcome by the other of the first (14) and second (13) gear elements when the injection device receives a collide along the predetermined direction (D) and the other one moving away from
