A cam pin (16) and a demating prevention pin (35) that are provided in a driving frame (15) and have an identical shape are allowed to mate with a cam groove (18) and a demating prevention groove (36) that are provided in a cam frame (17), respectively. A first protrusion (37) is provided on at least one side in an optical axis direction of a portion of the demating prevention groove (36) with which the demating prevention pin (35) mates when the driving frame (15) is advanced. When an external force is applied to the driving frame (15), a cylindrical portion (35f) of the demating prevention pin (35) and the first protrusion (37) come into contact with each other. This prevents the cam pin (16) from demating from the cam groove (18). The cam pin (16) and the demating prevention pin (35) are made of common components, making it possible to reduce the number of components.