To provide an adapter for on-vehicle device connection where a connection cable can be pulled out toward a desired direction, and preferable wiring layout, on the basis of relative positional relation between the adapter for the on-vehicle device connection and an on-vehicle device, can be performed.

An adapter for on-vehicle device connection comprises: a case body 2; a connection terminal 13 provided at a front surface of the case body and attached to a vehicle; a connection cable 15 pulled out to the outside from a back surface of the case body; a connection bush 14 capable of positively and negatively rotating the connection cable in an angle range set in a plane parallel to the back surface of the case body; and a circuit part incorporated in the case body and for electrically connecting the connection terminal to the connection cable.