The present technology relates to a signal processing apparatus, a control method, an image pickup element, and an electronic appliance that achieve the suppression of an increase in electric power consumption. The signal processing apparatus may be configured to control an amount of electric current at a differential stage in a comparison unit that compares signal levels of a plurality of signals and reduce the amount of electric current for a period other than this comparison period. For example, the amount of electric current may be reduced by turning off part of a group of switches each capable of disconnecting a path of an electric current from an electric current source. In addition, for example, the amount of electric current may be reduced by causing a gate potential at the electric current source unit to decrease. The present technology can be applied to, for example, an image pickup element and an electronic appliance.