A pulse width modulation (PWM) amplifier which is capable of reducing unwanted radiation from a PWM output thereof, which can cause EMI, while reducing manufacturing costs thereof. A triangular wave-generating circuit (3) of the PWM amplifier outputs a triangular wave. The triangular wave has a waveform steep or gentle in pulse rising and falling slopes dependent on a value of current flowing through an FET (116) or an FET (117). The value of current is changed by a current flowing through a FET (112). A switching element (32) changes voltage applied to the gate of an FET (110), for control of increase and decrease in the current flowing through the FET (112). This enables the triangular wave to be generated such that it is formed by pulses having different periods. An input signal is subjected to PWM amplification based on the triangular wave generated.