Many treatments require that patients undergo frequent intramuscular or subcutaneous injections at regular intervals e.g. daily, weekly or monthly.  To allow a patient to live a normal life it is common that he performs the injections himself.  For this reason, several devices have been developed with the particular aim to facilitate the injection process, for ergonomic as much as psychological reasons.  About the latter, one can easily conceive that the vision of the needle can frighten a patient.  Furthermore, the risk of injury or of contamination is critical, in particular for other persons having to handle the devices. 
To improve the safety of syringes, passive or active protection caps have been developed, allowing the needle to be hidden.  Nevertheless, this type of device brings no improvement to the functionality of the injection process and it is always for the patient, as with conventional syringes, to carry out manually the injection process. 
Some automatic injection devices offer a substitute for the patient in carrying out automatically the injection, after it is triggered.  There is in this way disposable devices.  Their cost is a major inconvenience in the case of treatment requiring frequent injections.  Furthermore, given that the device is single use, it is technically unsophisticated, in particular from the controls point of view, or from the electronic means that allow improvements to the functionalities. 
Devices use sometime conventional syringes, which is advantageous, because it allows for the combination of disposable components for the parts in contact with the medication, and components that can be perfected, because they are being kept from one utilization to another.  The treatment protocols are generally conceived so that the entire content of the syringe is injected in a single time.  However, it is necessary to perform many handling steps, before the injection, to remove the cap protecting the syringe, introduce the syringe into the device, then, after the injection, to remove the syringe from the device and replace the cap.  This type of device has the inconvenience that certain of the handling steps have to be carried out while the needle is not protected.  The handling of the used syringe and contaminated after injection exposes the hospital personnel or people surrounding the patient to risks of infection. 
Another type of device uses multi-dose cartridges of medication, which is susceptible to be used several times consecutively, the apparatus taking care to administer the correct quantity to the patient.  This type of apparatus can be safe for the patient and the persons handling it, because the injection needle is always hidden and does not present a risk of injury.  This type of apparatus is particularly sophisticated, in particular to ensure in a safe way the dosage of medication, but also to ensure its programming, depending on the treatment and the medication.  These apparatus are adapted for multi-dose cartridges, but cannot receive conventional syringes. 
The present invention aims to offer a device allowing the combination of the advantages of the above apparatus, whilst avoiding the inconveniences.  Particularly, the invention relates to a very safe device, advantageous from the cost impact on the treatment and which can be coupled with high-performance electronic means.