The invention relates to a device for dynamically adjusting volume within communication apparatus. The communication apparatus includes a speaker and an amplifier electrically connected to the speaker. The device is configured in the communication apparatus and includes a distance sensing unit and a signal processing circuit. The distance sensing unit is used for sensing a distance between the communication apparatus and a user to obtain a distance data. The signal processing circuit is used for dynamically adjusting a gain of the amplifier according to the distance data. The amplifier amplifies an input signal by the gain and then outputs an output signal to the speaker. Therefore, the output volume of the communication apparatus can be dynamically adjusted instead of being manually adjusted.