Provided is a control apparatus which is connected to an on-vehicle control device via an in-vehicle communication line, and constitutes, together with the on-vehicle control device, an in-vehicle network with the in-vehicle communication line being a transmission path. The control apparatus includes: a storage unit configured to store therein an update program for the on-vehicle control device; a monitoring unit configured to monitor an occupancy of the in-vehicle communication line; and a transfer control unit configured to control a timing to transfer the stored update program to the on-vehicle control device, on the basis of the occupancy being monitored.