The authentication device for saddled vehicle applied to a saddled vehicle including a FOB key that transmits an authentication signal, a control unit that receives and authenticates the authentication signal, a kick starter that starts an engine, and a generator that rotates in conjunction with an operation on the kick starter is configured such that, due to operating the kick starter, the engine is started, and electric power generated by the generator is supplied to the control unit, wherein the control unit stops the engine when the authentication signal is not authenticated before a lapse of a first predetermined time after the control unit is started.