A radio-frequency power amplifier for preventing a final-stage HBT from being destroyed is provided. To this end, a radio-frequency multistage power amplifier of the present invention includes: a first amplification stage having a first hetero bipolar transistor of which collector output is detected; a second amplification stage which is prior to the first amplification stage and which has a second hetero bipolar transistor in which the detection result is reflected; a first resistor provided between a collector of the second hetero bipolar transistor and a power supply; and a protection circuit which is connected between a collector of the first hetero bipolar transistor and the collector of the second hetero bipolar transistor, detects output from the collector of the first hetero bipolar transistor, and reduces a voltage of the collector of the second hetero bipolar transistor in accordance with the detected output.