A transimpedance amplifier circuit for an optical receiver in an optical communication system in which a range of an increase/decrease in bandwidth according to gain change is reduced by a bandwidth adjustor. The circuit includes: a photodiode (PD) for generating a current signal by photoelectric conversion of an input optical signal; a Transimpedance Amplifier (TIA) for converting the current signal input from the photodiode into a voltage signal; an auto gain adjustor for adjusting feedback resistances of the transimpedance amplifier; a photodiode parallel capacitor reducer for reducing a parallel capacitor current of the photodiode; and a bandwidth adjustor for reducing a range of an increase/decrease in bandwidth according to an increase/decrease in gain of the transimpedance amplifier.