To provide a mobile phone which can be used without hampering convenience in a condition where functions of the mobile phone are switched and can improve operability. The mobile phone includes an optical sensor, a display element, a pixel circuit portion where a plurality of pixels having a plurality of transistors are arranged in matrix, an optical sensor control circuit which is connected to an optical sensor driver circuit for driving the optical sensor and reads a signal from the optical sensor, a display portion control circuit which is connected to a display element driver circuit for driving the display element and outputs an image signal for displaying an image on a display portion, a gradient detection portion for outputting a signal in accordance with a gradient of the mobile phone, and an arithmetic circuit for performing display in the pixel circuit portion by switching image signals output to the display portion control circuit with a signal from the gradient detection portion.