A control system comprising: an in-vehicle device mounted in a vehicle; and at least one electronic key, wherein the in-vehicle device includes a transmission unit configured to transmit a first signal and a second signal to the electronic key, a first operation detection unit configured to detect an operation of locking a door of the vehicle, a determination unit configured to determine whether or not the electronic key is a control target electronic key determined in advance, the electronic key used to perform a locking operation detected by the first operation detection unit, and a first control unit configured to transmit the second signal from the transmission unit toward the electronic key determined as the control target electronic key, when the determination unit determines that the electronic key used to perform the locking operation is the control target electronic key, and the electronic key includes a reception unit configured to receive the first signal and the second signal from the in-vehicle device, and a second control unit configured to set a first mode until the reception unit receives the second signal, and set a second mode when the reception unit receives the second signal, the first mode being operating state for carrying out a process of receiving the first signal, the second mode being operating state for refraining from carrying out the process of receiving the first signal. an in-vehicle device mounted in a vehicle; and at least one electronic key, wherein the in-vehicle device includes a transmission unit configured to transmit a first signal and a second signal to the electronic key, a first operation detection unit configured to detect an operation of locking a door of the vehicle, a determination unit configured to determine whether or not the electronic key is a control target electronic key determined in advance, the electronic key used to perform a locking operation detected by the first operation detection unit, and a first control unit configured to transmit the second signal from the transmission unit toward the electronic key determined as the control target electronic key, when the determination unit determines that the electronic key used to perform the locking operation is the control target electronic key, and a transmission unit configured to transmit a first signal and a second signal to the electronic key, a first operation detection unit configured to detect an operation of locking a door of the vehicle, a determination unit configured to determine whether or not the electronic key is a control target electronic key determined in advance, the electronic key used to perform a locking operation detected by the first operation detection unit, and a first control unit configured to transmit the second signal from the transmission unit toward the electronic key determined as the control target electronic key, when the determination unit determines that the electronic key used to perform the locking operation is the control target electronic key, and the electronic key includes a reception unit configured to receive the first signal and the second signal from the in-vehicle device, and a second control unit configured to set a first mode until the reception unit receives the second signal, and set a second mode when the reception unit receives the second signal, the first mode being operating state for carrying out a process of receiving the first signal, the second mode being operating state for refraining from carrying out the process of receiving the first signal.