PURPOSE: To simplify an exposure control system by providing a varying means which varies the F number of a photometric system and a driving means which drives the varying means associatively with zooming.
CONSTITUTION: The photometry device is provided with the varying means which varies the F number of the photometric system and the driving means which drives the varying means associatively with zooming. Here, a zoom position indicated through the operation of a zoom switch is outputted from a zoom position output circuit 11 and a zoom cam plate driving unit 12 drives a zoom am plate 10 with the output to perform the zooming operation. Therefore, the F number of the light measurement system is varied associatively with the zooming and the F number of a photography system is controlled according to the variation in the F number of the photometric system, thereby eliminating the need for an arithmetic means for finding the F number variation of the photometric system associated with the zooming. Consequently, the exposure system is simplified.