A Doherty amplifier comprising: a first amplifier (9; 33) configured to amplify a first signal as an auxiliary amplifier in a case where a frequency of each of the first signal and a second signal is a first frequency, and to amplify the first signal as a main amplifier in a case where the frequency of each of the first signal and the second signal is a second frequency; a second amplifier (10; 34) configured to amplify the second signal as a main amplifier in the case where the frequency of each of the first signal and the second signal is the first frequency, and to amplify the second signal as an auxiliary amplifier in the case where the frequency of each of the first signal and the second signal is the second frequency; and a combiner configured to combine the first signal amplified by the first amplifier (9; 33) and the second signal amplified by the second amplifier (10; 34), wherein the second amplifier (10; 34) has a saturated output power which is larger than a saturated output power of the first amplifier (9; 33), and the combiner is configured to, in the case where the frequency of each of the first signal and the second signal is the second frequency, transform output impedance of the first amplifier (9; 33) so that an imaginary component in the output impedance of the first amplifier (9;33) is reduced; the combiner is configured to, in a case where the first amplifier (9; 33) amplifies the first signal as an auxiliary amplifier and the second amplifier (10; 34) amplifies the second signal as a main amplifier, increase an output reflection coefficient of the second amplifier (10; 34) by transforming the output impedance of the second amplifier (10; 34); and an increased amount of the output reflection coefficient of the second amplifier (10;34) is larger than a reduction amount of the output reflection coefficient of the second amplifier (10; 34) due to a difference between the saturated output power of the first amplifier (9; 33) and the saturated output power of the second amplifier (10; 34). a first amplifier (9; 33) configured to amplify a first signal as an auxiliary amplifier in a case where a frequency of each of the first signal and a second signal is a first frequency, and to amplify the first signal as a main amplifier in a case where the frequency of each of the first signal and the second signal is a second frequency; a second amplifier (10; 34) configured to amplify the second signal as a main amplifier in the case where the frequency of each of the first signal and the second signal is the first frequency, and to amplify the second signal as an auxiliary amplifier in the case where the frequency of each of the first signal and the second signal is the second frequency; and a combiner configured to combine the first signal amplified by the first amplifier (9; 33) and the second signal amplified by the second amplifier (10; 34), wherein the second amplifier (10; 34) has a saturated output power which is larger than a saturated output power of the first amplifier (9; 33), and the combiner is configured to, in the case where the frequency of each of the first signal and the second signal is the second frequency, transform output impedance of the first amplifier (9; 33) so that an imaginary component in the output impedance of the first amplifier (9;33) is reduced; the combiner is configured to, in a case where the first amplifier (9; 33) amplifies the first signal as an auxiliary amplifier and the second amplifier (10; 34) amplifies the second signal as a main amplifier, increase an output reflection coefficient of the second amplifier (10; 34) by transforming the output impedance of the second amplifier (10; 34); and an increased amount of the output reflection coefficient of the second amplifier (10;34) is larger than a reduction amount of the output reflection coefficient of the second amplifier (10; 34) due to a difference between the saturated output power of the first amplifier (9; 33) and the saturated output power of the second amplifier (10; 34).