To provide a mobile terminal device that can securely maintain effects on power saving and eliminate such an inconvenience that a back light turns off suddenly.

A control section incorporated in the mobile terminal device detects temperature change of a housing when a user holds the mobile phone in a hand or releases it based upon the detection signal of a temperature sensor 21 installed at the center part on the back side of the housing in the housing and nearby a case of the housing. The control section automatically turns on a liquid crystal display panel 3 and back lights 4 and 12 when the user has the mobile phone in the hand, and automatically turns off the liquid crystal display panel 3 and back lights 4 and 12 when the user releases the mobile phone.