The asymmetry of causation and backward causation are discussed. The problems are whether asymmetry of causation is objective or subjective, and what backward causation is. First, I survey and criticize three theories about causation: Dowe's fork theory, Menzies and Price's agency theory and Woodward's manipulability theory. Next, I insist that we should distinguish between causal process and causal direction, and that the former objectively exists but the latter does not. Third, I clarify what backward causation is if the causal direction does not objectively exist. I focus on the relative direction of temporal axis in causal process. Forth and finally, I would like to apply my theory to the problem of non-locality in quantum mechanics.