A semiconductor integrated circuit for an audio system includes a playback processing section for playing back at least an optical disk, a frequency measurement circuit for measuring a frequency of a radio signal from a tuner, a display control circuit for making a display device display at least the frequency of the radio signal, and a controller for controlling the playback processing section, the frequency measurement circuit, and the display control circuit, according to an external signal. The playback processing section, the frequency measurement circuit, the display control circuit, and the controller are formed on a single semiconductor chip.