A solid-state image sensor, comprising a plurality of circuit groups each of which can assume an operating state and a non-operating state, a storage unit configured to store an order of switching the plurality of circuit groups from the non-operating state to the operating state, and a control unit configured to receive, from outside the sensor, a control signal, common to the plurality of circuit groups, for switching the plurality of circuit groups from the non-operating state to the operating state, wherein after receiving the control signal, the control unit sequentially switches, according to the order stored in the storage unit, the plurality of circuit groups from the non-operating state to the operating state at an interval of a period corresponding to an integer multiple of a cycle of a clock signal.