To provide a wireless terminal device that can control so that the size of RWIN of an electronic device on a receiving side changes to an optimum value when hand-down (hand-off) from high speed communication to low speed communication occurs, and a method for controlling the same. A wireless terminal device 1 includes: a first communication unit (10) that is connected to a PC (101) and performs communication with a network (202) side at a first communication speed; a second communication unit (11) that is connected to the PC (101) and performs communication with the network (202) side at a second communication speed that is faster than the first communication speed, and a control unit (12) that reciprocally switches between the first communication unit (10) and the second communication unit (11).