The invention discloses an automatic detection device of a transponder. A master control module is used for controlling a passive transponder detection module to detect the strength of an uplink signal of a passive transponder, the frequency and phase of an uplink link signal and a message read-write status; the automatic detection device can further simulate LEU (Lineside Electronic Unit) equipment, and detect the operating status of an active transponder through an active transponder detection module so as to judge whether the active transponder and the passive transponder are in good conditions, therefore the traffic safety can be effectively guaranteed; in addition, the automatic detection device can simulate the active transponder to generate a rail passing signal to detect the responding status of the LEU equipment; meanwhile, according to the technical scheme, the detection of large-capacity transponders can be realized, and the detection of an existing European standard transponders can be compatible.