A high-frequency amplifying integrated-circuit device is provided in which variations of gain can be reduced and which can be manufactured at a low cost as compared with prior art devices. A high-frequency amplifying integrated-circuit device includes a semiconductor substrate; and a transistor which is formed on the semiconductor substrate and which has a plurality of first electrodes, a plurality of second electrodes, and at least one third electrode, a high-frequency signal input to the plurality of second electrodes being amplified by the transistor and output from the third electrode, wherein at least two first electrodes from among the plurality of first electrodes are each grounded via a capacitor, and the electrostatic capacitance values of the two capacitors are set at mutually different values.