Abstract: An object of the present invention is to provide a monitoring system, a monitoring device, and a construction machine each capable of improving the convenience for a user during monitoring while ensuring security related to the leakage of video data of a peripheral region. In a monitoring system 10 of the present invention, a monitoring device 30 reads information related to an access ID from a first authentication-related information display portion 208 arranged outside an operator's cab of a construction machine 20, using a second camera 300, and also reads information related to an access password from a second authentication-related information display portion 210 arranged in the operator's cab, using the second camera 300. The access ID may include a combination of the identification number of the construction machine 20 and a code representing the type of the construction machine 20.