An amplification device configured to switch between a first amplifying function that allows sound volume adjustment and a second amplifying function that does not allow sound volume adjustment, the amplification device comprising: an operating member configured to have a position changed when turned or slid to set a sound volume; a driver configured to cause the operating member to turn or slide; a storage unit, in the first amplifying function, configured to store a sound volume set value corresponding to a position set by the operating member, a signal processing circuit configured to, in the first amplifying function, amplify an incoming sound signal so that the sound volume corresponding to the position set by the operating member is obtained and, in the second amplifying function, amplify an incoming sound signal at a fixed amplification factor regardless of the position of the operation member; and a controller configured to control the signal processing circuit, wherein during execution of the first amplifier function, the controller is configured to control an amplifying operation of the signal processing circuit so that the sound volume corresponding to the position set by the operating member can be obtained, during execution of the second amplifier function, the controller is configured to turn off the sound volume adjusting function of audio amplifier thus preventing the audio amplifier from changing the sound volume even when the position of the operating member is changed, wherein, when the first amplifying function is switched to the second amplifying function and then the second amplifying function is switched back to the first amplifying function and at this time the sound volume set value corresponding to the position of the operating member is the sound volume set value corresponding to the position corresponding to a second sound volume larger than the sound volume set value stored in the storage unit corresponding to a first sound volume that was output right before switching from the first amplifying function to the second amplifying function, the controller is configured to change the position of the operating member to a position corresponding to a third sound volume smaller than the second sound volume, and to control the amplifying operation of the signal processing circuit to cause the signal processing circuit to output the third sound volume, the controller is configured to control the driver to turn or slide the operating member from the position corresponding to the second sound volume to the position corresponding to the third sound volume. an operating member configured to have a position changed when turned or slid to set a sound volume; a driver configured to cause the operating member to turn or slide; a storage unit, in the first amplifying function, configured to store a sound volume set value corresponding to a position set by the operating member, a signal processing circuit configured to, in the first amplifying function, amplify an incoming sound signal so that the sound volume corresponding to the position set by the operating member is obtained and, in the second amplifying function, amplify an incoming sound signal at a fixed amplification factor regardless of the position of the operation member; and a controller configured to control the signal processing circuit, wherein during execution of the first amplifier function, the controller is configured to control an amplifying operation of the signal processing circuit so that the sound volume corresponding to the position set by the operating member can be obtained, during execution of the second amplifier function, the controller is configured to turn off the sound volume adjusting function of audio amplifier thus preventing the audio amplifier from changing the sound volume even when the position of the operating member is changed, wherein, when the first amplifying function is switched to the second amplifying function and then the second amplifying function is switched back to the first amplifying function and at this time the sound volume set value corresponding to the position of the operating member is the sound volume set value corresponding to the position corresponding to a second sound volume larger than the sound volume set value stored in the storage unit corresponding to a first sound volume that was output right before switching from the first amplifying function to the second amplifying function, the controller is configured to change the position of the operating member to a position corresponding to a third sound volume smaller than the second sound volume, and to control the amplifying operation of the signal processing circuit to cause the signal processing circuit to output the third sound volume, the controller is configured to control the driver to turn or slide the operating member from the position corresponding to the second sound volume to the position corresponding to the third sound volume.