An aperture unit having an optical axis is provided, which includes a fixed portion having a first surface and an opening, a guiding element movably connected to the fixed portion and accommodated in the first accommodating space, a first blade movably connected to the guiding element and the fixed portion, and a driving assembly used for driving the guiding element to move for moving the first blade. A first accommodating space having a recessed structure is formed on the first surface. The opening is formed in the first accommodating space and has a recessed structure. The driving assembly is at least partially disposed in the opening.