In a gain variable amplifier, a carrier detection circuit system, and an infrared remote-control receiver using the gain variable amplifier or the carrier detection circuit system, to each of a positive output voltage Vo1 and a negative output voltage Vo2 of an amp to be subjected to gain control, connected is an AGC circuit output current (½) Iagc which is one-half of a gain control current and is a constant current. With this arrangement, it is possible to provide the gain variable amplifier, the carrier detection circuit system, both of which can reduce noise superimposed on the gain control current, and it is also possible to provide the infrared remote-control receiver using the gain variable amplifier or the carrier detection circuit system.