A communication terminal apparatus wherein even if there occurs a dropout or overtaking of call control messages, the current service can be continued without increasing the load of an apparatus such as a server in the network. In this apparatus, a VoIP call control part (103) performs call controls including both a call establishment of a VoIP telephone conversation using a wireless LAN system and a call disconnection thereof. A line switching call control part (104) performs call controls including both a call establishment of a line switching telephone conversation using a mobile communication (cellular) system and a call disconnection thereof. A handover part (105) determines the reception quality of the wireless LAN system and that of the mobile communication (cellular) system and controls, based on the determination results, the handover between the wireless LAN system and the mobile communication (cellular) system.