A holding device for holding an object having an opening includes: a first member inserted into the opening, having a cylindrical shape, and including multiple divisional portions divided by notches; and a second member including a shaft movable in the cylindrical shape and a head disposed on one end of the shaft and smaller than the opening and larger than an inner dimension of the cylindrical shape. Each divisional portion is expandable by the head so that the expanded divisional portion holds the object when the first member with the second member is inserted into the opening, and the first member is relatively displaced toward the second member.