A timing adjusting method detects a phase error between a main signal path from which a transmitting signal is obtained and a control signal path from which a voltage control signal is obtained, based on a to-be-amplified signal that is to be amplified and represents an amplitude or a power of the transmitting signal prior to amplification and a feedback signal that represents an amplitude or a power of the transmitting signal after the amplification, adjusts an amount of delay of at least one of the main signal path and the control signal path so as to mutually cancel the phase error, and amplifies the transmitting signal from the main signal path depending on the voltage control signal from the control signal path. The detecting the phase error may include detecting polarity transition points of a slope of a waveform of the to-be-amplified signal or the feedback signal, and measuring the phase error using the detected polarity transition points.