provided in the upper system depending on the design the absolute value as the reference value is set to the comparator 17 the signal processor 11 refers to the value set to the comparator 17 and instructs the amplitude variable unit 13 to reduce the input amplitude of the amplifier 141 such that the reflection coefficient b u2032 a u2032 falls below 1 for example in accordance with the instruction from the signal processor 11 the amplitude variable unit 13 performs the control to reduce the input amplitude of the one system such that the reflection coefficient b u2032 a u2032 falls below 1 for example alternatively the signal processor 11 refers to the value set to the comparator 17 and instructs the amplitude variable unit 13 to reduce the input amplitude of the amplifier 141 such that the reflection coefficient b u2032 a u2032 becomes equal to a predetermined value for example in accordance with the instruction from the signal processor 11 the amplitude variable unit 13 performs the control to reduce the input amplitude of the one system such that the reflection coefficient b u2032 a u2032 becomes equal t the predetermined value for example note that the predetermined value is determined in advance at the time of designing or the like however the predetermined value.