A Doherty amplifier comprising: a first input circuit having an electrical length of 180 × n degrees, wherein n is an integer greater than or equal to 1, at a first operation frequency of first and second signals that are signals to be amplified; a second input circuit having an electrical length of 90 degrees at the first operation frequency; a first amplification element for amplifying the first signal that has passed through the first input circuit; a second amplification element for amplifying the second signal that has passed through the second input circuit; a first output circuit having one end connected to an output terminal of the first amplification element and another end connected to a combining point for connecting the Doherty amplifier to a subsequent stage, the first output circuit having an electrical length of 90 degrees at the first operation frequency; a second output circuit having one end connected to an output terminal of the second amplification element and another end connected to the combining point and the other end of the first output circuit, the second output circuit having an electrical length of 180 × n degrees at the first operation frequency; a compensation circuit having one end connected to the other ends of the first and second output circuits and another end grounded, the compensation circuit having an electrical length of 90 degrees at the first operation frequency and an electrical length of 45 degrees at a second operation frequency which is half of the first operation frequency; a control unit for switching between operating classes of the first and second amplification elements (5, 6) when operation frequencies of the first and second amplification elements (5, 6) are the first operation frequency and operating classes of the first and second amplification elements (5,6) when the operation frequencies of the first and second amplification elements (5, 6) are the second operation frequency. a first input circuit having an electrical length of 180 × n degrees, wherein n is an integer greater than or equal to 1, at a first operation frequency of first and second signals that are signals to be amplified; a second input circuit having an electrical length of 90 degrees at the first operation frequency; a first amplification element for amplifying the first signal that has passed through the first input circuit; a second amplification element for amplifying the second signal that has passed through the second input circuit; a first output circuit having one end connected to an output terminal of the first amplification element and another end connected to a combining point for connecting the Doherty amplifier to a subsequent stage, the first output circuit having an electrical length of 90 degrees at the first operation frequency; a second output circuit having one end connected to an output terminal of the second amplification element and another end connected to the combining point and the other end of the first output circuit, the second output circuit having an electrical length of 180 × n degrees at the first operation frequency; a compensation circuit having one end connected to the other ends of the first and second output circuits and another end grounded, the compensation circuit having an electrical length of 90 degrees at the first operation frequency and an electrical length of 45 degrees at a second operation frequency which is half of the first operation frequency; a control unit for switching between operating classes of the first and second amplification elements (5, 6) when operation frequencies of the first and second amplification elements (5, 6) are the first operation frequency and operating classes of the first and second amplification elements (5,6) when the operation frequencies of the first and second amplification elements (5, 6) are the second operation frequency.