A state-of-device remote monitor system capable of applying a general-purpose line as a transmission line for transmitting detection signals of a state of a device, comprises an on-the-spot area, and a management area. The on-the-spot area includes an electric device, a detector for detecting a device state of the electric device, and a first communication signal converter for converting detection data obtained by the detection of the detector into communication signals, and transmitting the communication signals. The management area includes a second communication signal converter for converting the communication signals received from the first communication signal converter into the detection data before being converted by the first communication signal converter, a maintenance tool having a diagnostic/analytic program for analyzing the device state from the detection data converted by the second communication signal converter, and a maintenance database stored with data necessary for the analysis by the diagnostic/analytic program and a diagnosed result, and a display unit for displaying the diagnosed result obtained by the analysis by the maintenance tool.