To provide a mobile phone which estimates a surrounding noise level by utilizing extension functions other than a telephone function mounted thereon, and automatically regulates a received speech volume during a speech.

A data processing apparatus 1 starts a camera 32 during a speech and captures image data from the camera 32 by each prescribed timing. The data processing apparatus 1 compares two consecutive image data among the image data captured from the camera 32 and counts number of luminance dissident points between the both, and reads voice volume control data registered in advance in a setting storage section 21 by using the number of dissident points for a key to control a voice volume regulation section 41 thereby automatically regulating the voice volume from a receiver 42.