A diode linearizer according to the present invention has parallelly mounting linearizer core units on a RF signal path via capacitors between the RF signal path and a ground, thus does not need a switch using an FET, for example, at a time of selectively operating a plurality of linearizer core units. Moreover, the diode linearizer does not need a capacitor in series for blocking a direct current between RF signal input and output terminals. Thus, a range of a gain which can be compensated by the diode linearizer can be increased. Furthermore, an insertion loss of the RF signal path in a state where the diode linearizer is off can be reduced, and a range of a gain expansion in operation can be increased. The switch is not used, or the number of elements of the capacitors which are needed is small, thus a circuit size is also small.