A method for calibrating luminance of a display is provided which is capable of reducing power consumption in simple and low-cost configurations without putting a load on a CPU adapted to control each component of a portable electronic device. An amount of light corresponding to an amount of light incident on an organic EL display is measured and an output voltage is divided by an output voltage dividing section based on a light amount voltage being a result from the measurement and an output voltage is adjusted by the organic EL display power source based on the divided voltage.