An arbitrary threshold value (Ei0) is established which defines a boundary as to activating an RF-AGC circuit (21) if the value of the field intensity (Ei) of a received signal is greater than what value while the value of the field intensity of a signal at a desired frequency being a predetermined value (Ei0) in a weak field area. The established value (Ei0) is used to provide a threshold value establishing/controlling part (22) that controls the ON/OFF of the operation of the RF-AGC circuit (21). In this way, a set maker or the like of an IC including an automatic gain control part (11) can perform a field test or the like such that a preferable value obtained by a result of the field test or the like can be used as an AGC start level (Ei0), whereby an optimum AGC control can be performed based on the preferable AGC start level (Ei0).