An assisted manual injection device for injecting a composition contained in a container, wherein the container is provided with a needle at its distal end, and contains a piston, the injection device comprising: - a body comprising at least one gripping zone by which the body can be held in a user's hand, - a holding element of the container, configured to receive and hold the container in a stationary manner relative to the body, - an electromechanical system comprising: • a piston rod capable of being moved in translation in the container relative to the body of the device in order to move the piston, • an actuation system of the piston rod, • a processor capable of communicating with the actuation system, the device being characterized in that it comprises at least one force sensor positioned on the body at a gripping zone, the force sensor being configured to receive, as input, a mechanical effort F1 exerted on said sensor by the user during the injection of the composition, and to transmit to the processor an output signal F2 that depends on the mechanical force, and the processor is configured to send an instruction to the actuation system depending on the output signal from the sensor in order to actuate the piston rod depending on a predetermined control law, in order to adjust the mechanical effort that needs to be applied by the user to the piston rod in order to inject the composition. - a body comprising at least one gripping zone by which the body can be held in a user's hand, - a holding element of the container, configured to receive and hold the container in a stationary manner relative to the body, - an electromechanical system comprising: • a piston rod capable of being moved in translation in the container relative to the body of the device in order to move the piston, • an actuation system of the piston rod, • a processor capable of communicating with the actuation system, the device being characterized in that it comprises at least one force sensor positioned on the body at a gripping zone, the force sensor being configured to receive, as input, a mechanical effort F1 exerted on said sensor by the user during the injection of the composition, and to transmit to the processor an output signal F2 that depends on the mechanical force, and the processor is configured to send an instruction to the actuation system depending on the output signal from the sensor in order to actuate the piston rod depending on a predetermined control law, in order to adjust the mechanical effort that needs to be applied by the user to the piston rod in order to inject the composition. • a piston rod capable of being moved in translation in the container relative to the body of the device in order to move the piston, • an actuation system of the piston rod, • a processor capable of communicating with the actuation system, the device being characterized in that it comprises at least one force sensor positioned on the body at a gripping zone, the force sensor being configured to receive, as input, a mechanical effort F1 exerted on said sensor by the user during the injection of the composition, and to transmit to the processor an output signal F2 that depends on the mechanical force, and the processor is configured to send an instruction to the actuation system depending on the output signal from the sensor in order to actuate the piston rod depending on a predetermined control law, in order to adjust the mechanical effort that needs to be applied by the user to the piston rod in order to inject the composition.