An amplifier and a portable telephone apparatus using the same in which a resonance circuit is provided for each of different frequencies and bypass capacitors of the ground terminal of a transistor are properly switched according to the different frequencies. Two capacitors connected to each other in series for the parallel resonance circuits to be connected to the output terminal of the amplifying transistor are used for the resonance capacitors for the higher frequency. For the lower frequency, one of the tow capacitors that is on the ground side is used as a bypass capacitor that grounds the ground terminal of the transistor in a high frequency manner, the other capacitor being functioned as a resonance capacitor at that frequency.