PURPOSE: To set the lightness of a photographic picture plane to a value that a photographer intends by switching a stop device from an automatic adjustment state to a manual adjustment state through a clutch mechanism by the axial movement from the 1st position to the 2nd position.

CONSTITUTION: A switching device is provided with a switching operation means 8 which switches the stop device from the automatic adjustment state to the manual adjustment state through the clutch mechanism 14 by the axial movement from the 1st position to the 2nd position and allows the stop device 7 to be adjusted by rotation. Consequently, a push button 9 is only pressed in the automatic adjustment state to lock automatically the device at once, and a stop aperture is adjusted manually by the rotation of the changeover knob (switching operation means) 8. Consequently, the lightness f the photographic picture plane is set to a value that the photographer intends.