Noise on a current to be measured is removed. Horizontal power supply lines (PVDD) are arranged in a horizontal direction and supply a current to pixels in respective corresponding horizontal lines. A switch (8) connects a group of the horizontal power supply lines (PVDD) to a first power supply line (PVDDa) or a second power supply line (PVDDb) disposed outside a pixel region in a switchable manner. Only the horizontal power supply lines (PVDD) in a group to which a pixel to be measured belongs are supplied with power from the second power supply line (PVDDb) so as to measure a current of each pixel in the group, and a current flowing into a power source (PVDDa) connected to a group to which other pixels than the pixel to be measured belong is measured, to thereby calculate a pixel current based on a difference between the two measured currents.