Provided are a bearing and a medical device in which a gap is secured between an inner ring and an outer ring, and the gap can be used as a flow path for a fluid or an object. A bearing having a plurality of rolling elements between an inner ring and an outer ring is provided with a raceway surface on which the rolling elements roll on the outer ring and receiving portions for rotatably accommodating the rolling elements at a position of the inner ring facing the raceway surface.
