A portable information terminal device has a plurality of casings providing a front surface and a rear surface, respectively. The casings have walls defining spaces in which speakers are housed and thicker than walls thereof that define a space in which a component including an internal circuit is housed. The walls defining the spaces in which speakers are housed are prevented from causing resonance due to vibrations of the speakers. The walls that define the space in which the component including the internal circuit is housed may be of a minimum thickness required irrespective of resonance caused by vibrations of the speakers. With the above arrangement, the portable information terminal device is small in size and weight.