A control apparatus, an on-vehicle device and a method

A control apparatus is configured to control communication between an on-vehicle device and a device coupled to the on-vehicle device via a cable, the control apparatus comprising: a cable length detecting part configured to detect a length of the cable; and a communication controlling part configured to perform, based on the length of the cable detected by the cable length detecting part, control for ensuring communication quality between the on-vehicle device and the device.