Let us consider a closed vessel or chamber, which is rotating in prescribed manner, and inside which an ideal fluid is filled up. In this ideal fluid, flow will be set up, which is induced by motion of rotating vessel. In this report, the author has made some study about this flow, especially about effect of this fluid flow upon motion of vessel or chamber body. Thus, effect of fluid flow upon polar moment of inertia of this rotating vessel is studied. Next, taking up the case in which the vessel is made in form of fan-shaped closet, and considering the case of two-dimensional motion of ideal fluid, some detailed discussion is made, giving numerical examples. It is pointed out that effect of flow of the fluid can appear as phenomenon of virtual mass with regard to accelerated rotational motion of the vessel body.