Provided are a mobile station and an information delivery server that are capable of continuously providing a non-voice service, particularly a message service, even when being transitioned between areas of different radio access technologies. A UE (100) determines that an SMS over IP is in an unavailable state through communication via a radio access network. When a determination is made that the SMS over IP is in an unavailable state, even if the UE (100) is set to use the SMS over IP with higher priority than an SMS over NAS, the UE (100) uses the SMS over NAS to execute a short message service.