An input system for photographic cameras is provided with a plurality of input switches. The input system includes a matrix input circuit having a plurality of inputs corresponding to a plurality of outputs. A state detector scans key signals output from matrix input circuit at predetermined time intervals and detects states of respective switches provided in the camera so that the camera may operate according to these states. The time interval at which the key scan signals are output is adjustable depending on a state of a main switch. Specifically, the time interval may be relatively long when the main switch is in an OFF state and relatively short when the main switch is in an ON state. More specifically, when the main switch is in the ON state, the time interval of key scan should be adjusted relatively short so that the camera may rapidly operate in response to the states of the respective switches because the camera is ready for photographing in this state of the main switch. When the main switch is in the OFF state, on the other hand, the time interval of the key scan may be relatively long to suppress a consumption of a source battery, because the camera is not ready for photographing in this state of the main switch and it is unnecessary for the camera to operate rapidly.