In a portable radio terminal unit, when a built-in antenna is provided, influence of user's body is to be reduced as small as possible to prevent deterioration of antenna characteristics. The built-in antenna is arranged in contact with a microphone unit positioned at lower portion of a unit casing. The microphone unit is mounted on a front casing forming the casing. Therefore, the built-in antenna is also mounted on the front casing. Thus, even during calling and browsing display, the built-in antenna may not contact with a user's head or may not be covered by the user's hand to reduce deterioration of the antenna characteristics for maintaining more stable communication characteristics.