An amplifier has an N number of input networks connected to an input terminal to receive an input signal, a first amplifier to amplify one output signal from the N number of input networks, a (N−1) number of secondary amplifiers to amplify the remaining (N−1) number of output signals, except for the one output signal, from the N number of input networks, where the amplification order of the (N−1) number of secondary amplifiers is determined based on the power level of each output signal from the N number of input networks when the first amplifier is operational, an N number of output networks which are arranged, and a first bias network to supply a D.C. bias voltage to at least one of the N number of output networks. An electrical length of the first bias network is less than 90 degrees.