Amplifying device

An amplifying device includes: a signal splitter configured to split an input signal to a plurality of signals having a phase difference between the plurality of signals fluctuating in accordance with an absolute value of an amplitude of the input signal; a plurality of amplifiers configured to amplify the plurality of signals respectively; a combiner configured to combine the amplified plurality of signals to generate an output signal; a selector configured to select one of output signals whose phase is inverted or non-inverted; and a switch controller configured to control the signal splitter so that phases of the plurality of signals are non-inverted, and to control the selector so that the selector selects one of the output signals, in accordance with a first point of time when the absolute value becomes a minimum or a second point of time deviated from the first point by a predetermined time period.