Abstract: The pupil expander 1 of the present invention is used to maintain a pupil in an expanded state during ophthalmologic surgery such as, e.g., cataract surgery. The pupil expander 1 is equipped with four arm sections 10 arranged serially in a manner as to form a circular shape as a whole and joint sections 20 which connect end sections of adjacent arm sections in a movable manner. With this, since the end sections of adjacent arm sections 10 are connected in a movable manner and therefore the entire shape of the pupil expander 1 can be deformed in an eye via the joint section 20, the pupil expander can be arranged safely without damaging an iris I, which enables easy and assured maintenance of a sufficiently expanded state of a pupil.