An acoustic processing device (1, 1A), connectable to a first external equipment, a second external equipment and a third external equipment (5, 6, 7), the acoustic processing device (1, 1A) comprising: a controller; a signal input/output unit that is adapted to receive an input signal from the third external equipment (5, 6, 7) and to output a signal to the first external equipment in a standby through mode; a sound signal processing unit that is adapted to perform predetermined processing on a sound signal and to output the sound signal; a sound output terminal from which a sound is output to the second external equipment; a main power supply; and an auxiliary power supply, wherein the controller is adapted to perform the standby through mode which supplies power from the auxiliary power supply to the signal input/output unit, without causing the main power supply to supply power, in order to output the input signal from the third external equipment (5, 6, 7) to the first external equipment or the second external equipment, the controller is adapted to supply power from the auxiliary power supply to the sound signal processing unit as well in the standby through mode, and the sound signal processing unit in the standby through mode is adapted to extract the sound signal from the input signal which is input to the signal input/output unit from the third external equipment (5, 6, 7), to extract a high-frequency sound component and a low-frequency sound component from the sound signal, to output the high-frequency sound component through the signal input/output unit to the first external equipment, and to output the low-frequency sound component through the sound output terminal to the second external equipment. a controller; a signal input/output unit that is adapted to receive an input signal from the third external equipment (5, 6, 7) and to output a signal to the first external equipment in a standby through mode; a sound signal processing unit that is adapted to perform predetermined processing on a sound signal and to output the sound signal; a sound output terminal from which a sound is output to the second external equipment; a main power supply; and an auxiliary power supply, wherein the controller is adapted to perform the standby through mode which supplies power from the auxiliary power supply to the signal input/output unit, without causing the main power supply to supply power, in order to output the input signal from the third external equipment (5, 6, 7) to the first external equipment or the second external equipment, the controller is adapted to supply power from the auxiliary power supply to the sound signal processing unit as well in the standby through mode, and the sound signal processing unit in the standby through mode is adapted to extract the sound signal from the input signal which is input to the signal input/output unit from the third external equipment (5, 6, 7), to extract a high-frequency sound component and a low-frequency sound component from the sound signal, to output the high-frequency sound component through the signal input/output unit to the first external equipment, and to output the low-frequency sound component through the sound output terminal to the second external equipment.