PURPOSE: To obtain a vibration proof optical system provided with a variable apex angle prism device by which the occurrence of flare and ghost is reduced, the blurring of an image is corrected, and excellent optical performance is maintained by using a variable apex angle prism device having appropriate constitution.

CONSTITUTION: The variable apex angle prism device 1 constituted so that an optional prism apex angle is formed to perform prism action by sealing an optically transparent substance in a space formed by being interposed between two transparent optical members 2 and 5, and turning at least one of the members 2 and 5 by pressing force from the outside is attached to the front of a photographing lens 6. In the case of correcting the blurring of the image at the time of vibrating the lens 6 by changing the prism apex angle of the variable apex angle prism, the two members 2 and 5 are constituted of a meniscus-shaped lens whose convex surface is turned toward an object 9 side.