This paper discusses a philosophical answer about the question “in relativistic cosmology, is space really expanding?” In general cosmology which is called a big-bang theory, cosmological space is said to have been expanding like a balloon gradually pumped up since a big-bang, which is shown by a co-moving coordinate of which the scale gets bigger as a proper time of observers in the earth passes. In this paper, I would like to interpret this phenomenon from a structural spacetime realism's viewpoint in which spacetime is real as different whole structures for different coordinates you arbitrarily choose depending only on a metric/gravitational field. Through my remark, I get a new conclusion of what spacetime really means,thus the role of specetime in contemporary physics.