In this article the writer tries to make clear one of the main purports of the Tenth Book of the Laws, through reviewing the difference that Plato held to exist between his own proof of God's existence and his opponent's atheistic argument. Plato seems, in his argument for God, to imply that he has given up the physical viewpoint, from which every movement is seen going on endlessly, and, while using the same terms as the atheists, like "change" and "movement", he shows himself seeing the movement from quite a different angle, freed from the difficulties otherwise involved in the concept of the movement. Having wiped out the transitive aspect of the movement in the phenomenal world, he is reinterpreting the same movement as self-caused motion or life. When the atheists, as mechanistic materialists, see one movement inducing another or being induced by another, Plato would rather say that in reality both one and another are moving themselves successively by the participation in the original self-caused motion, just in the same way as a beautiful thing is said to be beautiful by its participation in the Idea of beauty. He himself writes that every thing in the world is full of life, because the life or the psychic operation is the same thing as the self-caused motion. Thus Plato established the priority of the soul to the material thing, and concluded that God exists as the first self-moving soul. The construction of Plato's proof consists of the three stages, starting from an experience of movement, which is seen as moving or moved, not in the narrow sense of the transitive verb, but in a wider sense implying a participation in some ultimate source, and then going back to the first self-moving soul, and lastly from this original soul explaining deductively every thing in the world. Almost the same argument, however, is seen on the side of the atheists. They also start from an experience of movement, which, however, they conceive only in the transitive sense and as induced from outside, and then trace back along the series of such induced motions to the ultimate elements or atoms-atoms, to which they also, just as the atomists did, would finally have reduced the elements, and which would be also self-moving at least in their empirical eyes-, and lastly they reconstruct from these sources every thing in the world. Therefore, the significant difference between Plato's proof and atheistic argument is after all only that of the starting points, whether a movement is seen from the physical angle, or from the "super-physical" angle. Otherwise the two arguments are the same both in logical structure and in persuasiveness. From these considerations, the writer concludes: Plato's argument for God here, so far as it pretends to have "refuted" the opponent who would not accept Plato's premiss, must be said to be somehow forced, though it can be valid enough in the eyes of the man who will start from the same premiss as Plato did; Plato's main task in this Book, however, must have lain rather in urging people to change their viewpoints, from the empirical to the broader one, so that they can retrace by their own reflection to the first cause of the world, Gcd; and his "refutation" of the atheists seems to have been no more than an atempt to carry out this main task of his.