A calculation output unit of a digital amplitude modulation device calculates and outputs a protection index of an amplifier based on a combined output signal or an amplitude modulation signal. A first protection unit outputs to a control unit a first control signal to place an entire amplifier unit in an off-controlled state, based on the protection index. A second protection unit outputs, to the control unit, a second control signal to control an upper limit number of amplifier units that can be on-controlled in parallel and a third control signal to on/off control the upper limit number or less or the initial number of the amplifiers. The control unit on/off controls the power amplifiers based on an input sound signal, the first control signal, the second control signal, and the third control signal.
