Provided are an underground installation support device improving installation workability of a support member supporting an underground installation and a method of manufacturing the support device. A support device 100 according to the disclosure is a support device 100 supporting an underground installation (a communication cable 700) and including a vertical frame member 20 that extends in a substantially vertical direction, lateral frame members 30A and 30B that are attached to the vertical frame member 20 and extend in a substantially horizontal direction, and an installation support member 40 that is attached to the vertical frame member 20 and the support device is disposed on a bottom portion (a bottom wall 505) of an underground cavity (a manhole 500).