A vehicular audio-amplifier controller comprising: a control circuit that comprises a delay buffer, a first processing unit of the control unit (3, S103, S4), a second processing unit of the control unit S104, S5), a power supply controller (7, S105, S11), and a sound signal output unit (3, S13); and a voltage acquisition unit that is configured to acquire a voltage value of a vehicular power supply (+VB) and a power-supply voltage (Vdd) that is supplied to an audio amplifier and to output information on the acquired voltages to the control circuit, wherein the delay buffer is configured to store a sound signal supplied from an audio signal source (5, 9a through 9c); the first processing unit (3, S103, S4) is configured to apply an absolute value process to the sound signal stored in the delay buffer, thereby converting the sound signal stored in the delay buffer into an absolute value, the absolute value constituting a processing result of the first processing unit (3, S103, S4); the second processing unit (3, S104, S5) is configured to apply a low-pass filter process and an offset process to the processing result of the first processing unit (3, S103, S4); the power supply controller (7, S105, S11) is configured to perform control of the power-supply voltage (Vdd) that is supplied to the audio amplifier based on the voltages acquired by the voltage acquisition unit and at least in accordance with a signal value processed by the second processing unit (3, S104, S5) and a type of the audio signal source (5, 9a to 9c), wherein the control circuit is configured to determine the type of the audio signal source (5, 9a to 9c); and the sound signal output unit (3, S13) is configured to output the sound signal stored in the delay buffer with only a delay time (Tdelay) that is determined based on a power supply control process time of the power supply controller (7, S105, S11). a control circuit that comprises a delay buffer, a first processing unit of the control unit (3, S103, S4), a second processing unit of the control unit S104, S5), a power supply controller (7, S105, S11), and a sound signal output unit (3, S13); and a voltage acquisition unit that is configured to acquire a voltage value of a vehicular power supply (+VB) and a power-supply voltage (Vdd) that is supplied to an audio amplifier and to output information on the acquired voltages to the control circuit, wherein the delay buffer is configured to store a sound signal supplied from an audio signal source (5, 9a through 9c); the first processing unit (3, S103, S4) is configured to apply an absolute value process to the sound signal stored in the delay buffer, thereby converting the sound signal stored in the delay buffer into an absolute value, the absolute value constituting a processing result of the first processing unit (3, S103, S4); the second processing unit (3, S104, S5) is configured to apply a low-pass filter process and an offset process to the processing result of the first processing unit (3, S103, S4); the power supply controller (7, S105, S11) is configured to perform control of the power-supply voltage (Vdd) that is supplied to the audio amplifier based on the voltages acquired by the voltage acquisition unit and at least in accordance with a signal value processed by the second processing unit (3, S104, S5) and a type of the audio signal source (5, 9a to 9c), wherein the control circuit is configured to determine the type of the audio signal source (5, 9a to 9c); and the sound signal output unit (3, S13) is configured to output the sound signal stored in the delay buffer with only a delay time (Tdelay) that is determined based on a power supply control process time of the power supply controller (7, S105, S11).