I have tried, in this paper, to make it clear how J. S. Mill had been confronted with Christianity by meeting with his different acquaintances and discussing religious matter with them. I have divided the developmental period of his religious ideas toward Christianity into three periods, and described the changes of Mill's ideas against Christianity.
In the first period, Mill was acutely critical against Christianity in his essay such as "On Religious Persecution" in 1824. In the second period, Mill became acquainted with John Sterling and Thomas Carlyle from 1825 to 1834, and was influenced by Romanticism. So he softened his criticism against Christianity. In the third period, Mill rather returned to what he had started from, and he considered Christianity from the viewpoint of External Utilitarianism.
In the last place, I have dealt with Mill's criticism of the traditional arguments for existence of God by comparing his critical argument against existence of God with his a$rmative proof of the Principle of Utility. I have concluded that if we accept Mill's proof of the Principle of Utility, then we are obliged to accept the traditional arguments of existence of God also.