Electronic Control Device and Electronic Control System

An object of the present invention is to provide an electronic control device and an electronic control system capable of achieving power supply redundancy while suppressing an increase in number of wirings. The present invention is an electronic control device including a data processing circuit that performs data communication with one or more another electronic control devices, the electronic control device including: a power source terminal connected to a first power source ; a first data terminal to which a first external data line is connected; and a power source selection circuit that has an input side to which the power source terminal and the first data terminal are connected and an output side to which the data processing circuit is connected, selects any one with a higher potential of power from the power source terminal and the first data terminal on the input side, and connects the selected one to the data processing circuit on the output side.