A comparator includes a first amplifier, a second amplifier, and a level holding part. The first amplifier includes differential-pair transistors and outputs a signal of a level corresponding to a comparison result from a first output node. The differential-pair transistors compare a reference voltage with a potential of an input signal. The second amplifier gain up the signal output from the first output node of the first amplifier and outputs the signal from a second output node. The level holding part holds a level of the second output node at a predetermined level. The second amplifier includes a transistor for amplification and a transistor for a current source. The level holding part holds the level of the second output node of the second amplifier such that the transistor for the current source does not fall into a level at which a saturated operation condition is not satisfied.