Lighting and/or signalling device for an automobile, assembled by stacking

The device (1) has an enclosure formed by a case (2) and lens (5), and receiving a support (3) that supports a light source and reflector (4). The case and lens are provided with a supporting unit (31) that is supported on the support or the reflector or a support-reflector assembly. Another supporting unit (22) is supported on the support or reflector or support-reflector assembly. The supporting units fix the support or reflector or support-reflector assembly along a direction (X) to apply mechanical action e.g. flexing. An independent claim is also included for a device assembling method.