The present disclosure relates to a comparator, an AD converter, a solid-state imaging apparatus, an electronic apparatus, and a method of controlling a comparator each of which enables power consumption to be reduced while a decision speed of the comparator is enhanced. A comparator, including: a differential input circuit operating at a first power source voltage, and outputting a signal when a voltage of an input signal is higher than a voltage of a reference signal; a positive feedback circuit operating at a second power source voltage lower than the first power source voltage, and speeding up a transition speed when a comparison result signal representing a result of comparison in voltage between the input signal and the reference signal is inverted; and a voltage converting circuit. The present disclosure can be applied to an ADC or the like arranged for each pixel of a solid-state imaging apparatus.