A resonance circuit comprising, for example, an inductor and a plurality of capacitors is provided as a load of a transistor. The capacitors are changed over by a switch. As the capacitors are changed over by the switch, a resonance frequency is changed according to the invention the frequency hopping of an input signal. To cancel ringing that occurs at the time of the switching action, a transistor which cancels gate feed through is added to the switch. An inductor is provided at the gate in order to suppress a gain reduction and an increase in noise factor in a high-frequency range. This provides a compact, wide-band amplifier which has low noise, a wide gain and low power consumption.