An electronic control device includes a plurality of control circuit units, a signal line, and a sneak-in suppression circuit. The plurality of control circuit units are connected to separate grounds, respectively. The signal line connects a first control circuit unit and a second control circuit unit. When a system is defined as a combination of a component and a ground corresponding to a control circuit unit, the sneak-in suppression circuit suppresses a sneak-in of electric power from the ground of one system (i.e., a subject system) to the other system connected by the signal line for preventing a cascading failure.