To provide a maintenance support system that can adapt to various terminal devices and easily acquires detailed state information and locates an anomaly cause about a target device.

A support terminal device 2, which is connected to a target device 1 having communication means and communicates with a support server 3 via a network 4 to diagnose and maintain the target device, comprises first communication means 21 adapted to communicate with the communication means of the target device, inquiry means 22 for inquiring and acquiring information from the target device, a second communication means 23 adapted to communicate with the support server, and an information acquiring means 26 for exchanging inquiry information from the support server with the inquiry means and a display means 24 to acquire information answering the inquiry from the inquiring means and an input means 25, and sending the information to the support server. The support terminal device and the support server adapted to communicate with the support terminal device via the network are combined to configure the maintenance support system.