The process of finding the antecedent of zero pronoun, that is indispensable to Japanese language understanding, is the topic of this paper. Here we mainly concern with discourses comprising two sentences that are in a subordinate relation, especially one of them describes the agent's volitional action and the other describes the reason of the action. We propose basically two new principles: (1) The agent of an action should experience a certain psychological reason, (2) Predicates reporting someone's psychological state are categorized into 1) weakly or 2) strongly bound to the expected point of view. Combination of these principles accounts for some problematic Japanese zero anaphora, which cannot be accounted for by the theories so far proposed.