An apparatus includes a detection unit including a plurality of pixels that are arranged in a matrix and that are divided into at least first and second pixel groups, a signal processing unit including first and second readout circuits and first and second A/D converters, a power supply unit configured to supply the components included in the signal processing unit with respective biases, and a control unit configured to control at least one of the signal processing unit and the power supply unit. The control unit is configured to perform processing of altering an analog signal capable of being input into at least one of the first and second A/D converters or altering an A/D conversion characteristic of at least one of the first and second A/D converters.