The present invention provides a tuner apparatus operating as a common tuner capable of receiving both satellite digital TV and terrestrial TV broadcasting. A tuner configured, according to the invention operates as follows. As the tuner apparatus receives satellite TV broadcasting, intermediate-frequency signals SIF1 are supplied to its quadrature detector circuit where the SIF1 signals are demodulated into baseband signals SI and SQ by using oscillation signals supplied thereto from its oscillator. As the tuner apparatus receives terrestrial TV or CATV broadcasting, terrestrial TV or CATV broadcast wave signals are supplied to its mixer circuit where these signals are frequency-converted into intermediate-frequency signals SIF1 that fall within the bandwidth of the satellite TV broadcasting SIF1 signals. The first intermediate-frequency signals SIF1 are supplied to the quadrature detector circuit where the SIF1 signals are frequency-converted into second SIF2 signals by using oscillation signals supplied thereto from the oscillator.