With the introduction of the above described capabilities, the comparator 12 surely generates a reset pulse Within a predetermined time period in consideration of the phenom enon that the ramp signal Ramp11 gradually rises While the sWitch S1 is ON. The sWitches S1 and S2 are respectively turned off and turned on With this reset pulse, so that the boost capacitor Cx is sure to be charged. That is, the driver D1 can alWays drive the sWitch S1 according to the state of the latch circuit 5.