Abstract: An automatic exposure device having an exposure sensor and a microprocessor includes a plurality of shuris wings each having a window of a given shape to be movable in respect to each other a motor controlled by the microprocessor for driving the movement of the plurality of shuris wings, an encoder disc for sensing a state of revolution of the motor, a counter for transmitting the state of revolution to the microprocessor by checking an encoder value recorded in the encoder disc, and a ROM table connected to the microprocessor for storing the encoder value and an exposure value corresponding to the encoder value.