In a photosensor in the pixel region of an active matrix substrate, the potential of a storage node is read out to output wiring as sensor circuit output, the potential of the storage node having changed in accordance with the amount of light received by a photodetection element in a sensing period, the sensing period being from when a reset signal (RS) is supplied until when a readout signal (RW) is supplied. A sensor startup period whose length is greater than or equal to the length of the sensing period is provided after a sensor data unnecessary period in which the sensor circuit output is not necessary, and furthermore before a valid sensor data period in which the sensor circuit output is necessary, and the sensor circuit output is read out in the valid sensor data period from the photosensor to which the reset signal was applied in the sensor startup period.