In Chapter XXVI of <i>The Principles of Psychology</i>,William James tries to argue for the existence of "will" using a physiological concept of the reflexive action. His argument of "will" seems to consist of the two seemingly conflicting standpoints, of which one is a physiological psychology and the other is an introspective psychology. The former enables him to discard the dualism of mind and matter and to connect the voluntary actions with the reflexive actions, the latter proving the existence of mind's functions, that is, to choose an object of mind and to make an effort to attend to it. In the last analysis, James' conception of mind could be thought of as the teleologically interpreted reflexive arc. <br>This paper is intended to deal with the relationship of these psychological schemes and his theism, which is described in the papers included in <i>The Will to Believe</i>, such as "Reflexive Action and Theism","The Dilemma of Determinism", and so on. His concept of "God" is a relative and functional term as his concept of "self" is. So his theism is not a traditional one, but something like an indeterministic world-view, which permits "chance" or "effort" to contribute, for its part, to the future of the world.