A thermoforming apparatus for making a container (2) by thermoforming a thermoformable film (3). The thermoformable film (3) and the container (2) obtain comprise at least one first layer (4) of plastic material in which an indicator is distributed which emits electromagnetic radiation in an expected response band when it is excited with electromagnetic radiation in a predetermined excitation band. The thermoforming apparatus (1) comprises: a thermoforming device (6), for thermoforming the thermoformable film (3); a feeding device (17); a conveyor (18); a checking device (19), operatively associated with at least one of either the thermoforming device (6) or the conveyor (18), for detecting defects (7) of the first layer (4) of plastic material in the container (2). The checking device (19) comprises: an emitter (20) for emitting towards the container (2) electromagnetic radiation in the predetermined excitation band; a detector (21) for receiving electromagnetic radiation emitted in the expected response band by the container (2); an electronic processing unit for receiving from the detector (21) information about the electromagnetic radiation received, and programmed to determine the presence or absence of defects (7) in the first layer (4) of plastic material of the container (2), by processing the information.