Schopenhauer, emphasizing those affinities between his own philosophy and Buddhism, was a thinker having played a leading role in the formation of ‘European Buddhism’. However, the ‘Schopenhauerian Buddhism’ is a distorted one by ‘pessimism’ and ‘denial of the will’ which constitute his metaphysics of the will. Schopenhauer includes as evidence of denial of the will Christianity, Brahmanism, Buddhism, quietism, asceticism, mysticism, and so forth,―which is the integration theory based on the concept of denial of the will. In that theory, Buddhism is defined as another pessimistic religion teaching denial of the will. In this sense, for him, Buddhism is intrinsically identical with Christianity, Brahmanism, mysticism, and so forth. The source of such distortion lies in his maintained essentialism. Schopenhauer’s essentialism conflicts with Buddhism’s anti-essentialism in the depths of thought. I will elucidate the in-depth disparities between his metaphysics of the will and Buddhism by comparing the former with the latter’s tilakkhaṇa and nibbāna. In this process, it is to be revealed that it is impossible to integrate Buddhism with Christianity, Brahmanism, mysticism, etc.