A smart entry system that releases a lock of an opening/closing body includes: a transmission unit that transmits a call signal to a mobile key by wireless communication; a reception unit that receives a response signal from the mobile key responding to the call signal; and a control unit that outputs a call signal transmission command to the transmission unit, performs authentication of the response signal when the reception unit receives the response signal, and outputs a command for unlocking the opening/closing body based on a result of the authentication. The call signal is transmitted by a polling system. The control unit includes an output strength setting unit that changes and sets an output strength of the call signal.