To prevent a user with an active mobile unit from getting in a car.

A communication system includes a mobile unit, and a control device that executes predetermined control on the basis of a signal from the mobile unit. The mobile unit includes an unlocking request signal transmission control part that executes a control to transmit an unlocking request signal to cause a vehicle with the control device to perform unlocking. The control device includes a control part that executes a control to stop operation of the mobile unit mounted on the vehicle when the unlocking request signal is transmitted from the mobile unit.