A smart key system includes a first transmitting unit, a first receiving unit, and a certification unit that are mounted on a vehicle, and a second receiving unit and a second transmitting unit that are mounted on a portable device. The certification unit performs certification processing of the portable device when the first receiving unit has received a reply signal. The first transmitting unit transmits the polling signal at a transmission timing that is later or earlier than a transmission timing based on the polling signal before the predetermined manipulation is performed, by a predetermined time shorter than a predetermined transmission cycle, when the predetermined manipulation has been performed in a situation where the certification unit does not certify the portable device.