A device is provided for measuring the differential pressure in anesthetic dispensing devices, with which the differential pressure can be measured between two lines for supplying gaseous components to a mixing site. A nickel metal film is formed on the substrate area including the source and the drain region. The detector is constructed to be segmented in the x-ray penetration direction so as to optimize count rate performance as well as avoid saturation. This compensation circuit eliminates the need for gate biasing capacitors, and provides flexibility in setting threshold voltages in low voltage circuits. The source line driver section generates a second drive signal of the source line based on the output from the second DAC, and then generates a first drive signal of the source line based on the output from the first DAC within one horizontal scan period.