A smart key system according to the present invention controls operations of devices mounted in a vehicle based on wireless communication between a control device mounted in the vehicle and a portable electronic key, and the control device includes a transmission circuit configured to output a request signal a predetermined number of times at predetermined times within a predetermined period in order to confirm authentication communication between the control device and a communication unit of the portable electronic key, and a communication mode switching unit configured to switch an authentication communication interval or an authentication communication time within the predetermined period of the request signal output from the transmission circuit of the control device if the authentication communication is not performed for a predetermined amount of time.