A radio communication device enabling a serial interface to restart transmission in a short time when interface setting is changed, as well as a method for controlling RF-BB state in the device, are provided. According to the radio communication device in which a radio frequency section (20) and a baseband section (10) are connected through a serial interface, exclusive signals (Act, Act_Ack) for triggering an interface state change and for acknowledging it are provided between the radio frequency section and the baseband section, respectively. Interface state change control is performed by transmitting and receiving the interface state change trigger exclusive signal and its acknowledgement exclusive signal between the radio frequency section and the baseband section.