The present invention provides an acoustic processing device capable of providing a high-quality sound even in a standby through mode. A controller is characterized by supplying power from an auxiliary power supply to a sound signal processing unit in the standby through mode. In the standby through mode, the controller extracts a sound signal included in an input HDMI signal, outputs a high-frequency sound component from an input/output unit to, for example, a television, and outputs a low-frequency sound component from a sound output terminal to a speaker (for example, a subwoofer) with an amplification function. As a result, the user can listen to content with powerful bass on the television, without operating an amplifying circuit, which consumes most of the power consumed by the acoustic processing device, using a main power supply, that is, while suppressing the power consumption of the acoustic processing device.