Provided is a comparator circuit that is capable of operating at high speed and canceling an offset voltage with high precision. The comparator circuit includes a second amplifier circuit for amplifying an output of an amplifier circuit and feeding back the amplified output to an input of the amplifier circuit. When the comparator circuit samples the input voltage, the second amplifier circuit conducts feedback and increases a gain to cancel the offset. Also, when the gain of the amplifier circuit is made lower than the gain of the second amplifier circuit, and the comparator circuit compares the input voltage, the comparing operation can be conducted at high speed by separating the amplifier circuit from the feedback of the second amplifier circuit.