Disclosed are a mobile communication device and mobile communication method which make it possible to reduce the amount of the data transfer during heterogeneous network handover processing in the hard handover processing in a mobile network. The mobile communication device which is equipped with a plurality of kinds of radio communication interfaces, receives a request to perform the handover between heterogeneous networks, which requests switching from a radio communication interface in use to another radio communication interface from the mobile communication network, and performs the handover between the heterogeneous networks comprises a measurement processing section (106) for measuring the connection quality of the plurality of kinds of radio communication interfaces, a handover execution predicting section (107); for predicting whether or not the handover between the heterogeneous networks is performed on the basis of the connection quality, and a TCP window control unit (113) for setting a window size to a smaller window size than the window size in use if the handover execution predicting section (107) predicts that the handover between the heterogeneous networks is performed.