In an amplifying circuit using a grounded-emitter high frequency signal amplifying bipolar transistor, the value of impedance of a bias circuit as seen from the base terminal of the bipolar transistor is made optimum in the baseband frequency. More specifically, the resistance value of a base ballast resistor R.sub.bias connected to the base terminal of the bipolar transistor is set to a range within .+-.50% of [V.sub.t/I.sub.bq-(.beta.R.sub.e+R.sub.b)] being "ideal resistance value", where I.sub.bq is static base current, .beta. is the gain of the transistor, R.sub.e and R.sub.b are parasitic resistance of the emitter terminal and base terminal, respectively, and V.sub.t is voltage defined by (kT/q).
