PURPOSE: To provide a new exposure controller capable of photographing while blurring a background except an object without the blurring of the object even when photographing the object of high luminance.

CONSTITUTION: A diaphragm device 12 is constituted of a transmissivity variable filter, the device is provided with a driving circuit 18 for varying the transmissivity of the filter, and the transmissivity of the diaphragm device and the stopping state of the diaphragm device are varied in accordance with a photographing condition. The transmissivity of the filter is controlled by the driving circuit 18 so that the transmissivity may become the smallest one at normal photographing, and when the luminance of the object is high, the transmissivity of the filter is increased in accordance with the result which is obtained when the stopping state is detected by a diaphragm position detector 19 and also the diaphragm is fully closed, so that the occurrence of a diffraction phenomenon is prevented. Also, at the time of photographing with a background blurred, the diaphragm 12 is fully closed by a driving circuit 7 and also the transmissivity is varied by the driving circuit 18.