A transmission device that includes a fixed support for receiving an electronic appliance. The transmission device has at least one first and one second retaining elements defining between them a receiving space, the second retaining element being movable with respect to the fixed support along a main direction so as to give the possibility of adapting the size of the receiving space. The transmission device includes a transmission element attached to the retaining elements by a mechanism that includes a first return element connecting the transmission element to the first retaining element and a second return element connecting the transmission element to the second retaining element. The stiffness of the first return element is equal to the stiffness of the second return element.