The present invention provides a structure in which an amplitude-modulation mode and a frequency-modulation mode are switched. A semiconductor device of the invention has: a reset control circuit to which a modulation mode select signal which selects an amplitude-modulation mode or a frequency-modulation mode and Manchester-encoded information are input, which outputs a first reset signal and a second reset signal; a first frequency-dividing circuit to which a carrier wave is input, which outputs a sub-carrier wave responding to the amplitude-modulation mode or a frequency-modulation signal responding to the frequency-modulation mode, according to the first reset signal; a second frequency-dividing circuit which outputs a basic clock of which a duty ratio is different between the amplitude-modulation mode and the frequency-modulation mode, according to the second reset signal and an output of the first frequency-dividing circuit; and an ASK/FSK switching portion to which an output from the first frequency-dividing circuit and Manchester-encoded information are input, which outputs an amplitude-modulation signal or a frequency-modulation signal according to the modulation mode select signal.