According to the present invention, there is disclosed a radio transmitter comprising: a signal processing section which outputs a control signal for designating one of first and second communication systems and a base band signal; a frequency synthesizer for outputting an LO signal corresponding to the control signal; a quadrature modulator into which the base band signal and LO signal are inputted; a first terminal for the first communication system; a second terminal for the second communication system; a first radio section which is disposed between the quadrature modulator and the first terminal and corresponds to the first communication system; a second radio section which is disposed between the quadrature modulator and the second terminal and corresponds to the second communication system; and a switch which passes an output signal from the quadrature modulator through any one of the first and second radio sections in response to the control signal.