<p>The purpose of the present invention is to provide a mobile terminal device that: suppresses the generation of echoes and howling that cause a deterioration in call quality; and achieves good call performance. The mobile terminal device (100) comprises a rear surface casing (120) and a battery cover (130) that covers the entire rear surface of the rear surface casing (120). Sound holes (125) for a microphone (170) and speaker sound holes (124) for a speaker (150) are arranged on the same rear surface of the rear surface casing (120). The rear surface casing (120) comprises a concave groove section (129), at least on the speaker (150) side and around the sound holes (125) for the microphone (170). The battery cover (130) comprises a convex protruding section (139) that fits into the groove section (129).</p>
