The invention relates to a trailer for traffic monitoring. By virtue of the trailer, a plurality of methods for detections and file records of red light and/or speed violations can be applied. A fundamental object of the invention is to provide a device capable of being disposed in any place, so that the device can carry out the detections and file records of the red light and/or speed violations, wherein the device does not aim to be installed in one passenger vehicle. The object is realized by using the trailer (1) for traffic monitoring through the following facts, that is, a mechanism capable of making the wheels (4) lifted and lowered is existed; at least one system used for carrying out the detections and file records of the red light and/or speed violations is arranged in this mode; and the mode enables the system to be integrated into the body (2).