To provide a signal transmission device enabling the number of signal lines to be reduced.

An inhibitor switch 1 for an automobile having six settings is equipped with a reference contact 11 connected to an ignition power supply and setting contacts 12 corresponding to the six settings. An output device 10 has six input terminals 14 connected to the six setting contacts 12, respectively, a reference resistance R connected to a meter 6 and to an automatic control unit of the automobile, and six dividing resistances connected between an output terminal 13 and the input terminals 14 and having resistance values differing from each other. A voltage obtained by resistance-dividing a difference voltage between a battery power potential and a ground potential by the reference resistance plus one of the dividing resistances is outputted to the output terminal 13. The output device 10 is connected to the meter 6 by harness 2, 5 having one signal line.