In Wittgenstein's diaries, manuscripts, and so on, he makes numerous references to religion. From this, we can see that Wittgenstein had a strong interest in religion, and that this interest continued consistently right from his `early phase' to his `late phase.' However, these are no more than fragmentary writings, and they do not go so far as to clearly indicate exactly what Wittgenstein's religious understanding was. In this paper, in order to pursue the essence of Wittgenstein's interest in religion, and to clarify the characteristics of his religious understanding, I focus on Tolstoy, who exerted a powerful influence on Wittgenstein. By considering Wittgenstein's religious understanding centered on the influence exerted by Tolstoy on him, we see that, for Wittgenstein, religion was truly an` issue of life.' Accordingly, Wittgenstein's religion can be called a `religion of life.'