Provided is a device capable of assisting a periodical motion of a creature, such as a human, by applying a force to the creature so as to match a motion rhythm and a motion scale of the periodical motion to a desired motion rhythm and a desired motion scale, respectively, while reducing computation processing load. The system has a sample container including a cover portion formed to be detachably mountable to a base portion, the sample stage on which the container is detachably mountable, and cover mountingdismounting apparatus for mounting and dismounting the cover portion from outside the sample chamber. Interconnected solar cells are positioned adjacent a rear surface of the transparent encapsulant layer to form a solar cell assembly.