根據效用主義的看法，快樂（happiness）是人類的終極價值，外顯行為的目的在於避苦求樂，故快樂追求係驅策行為之根本。本文藉由現金利得與捐贈議題的實驗，驗證于席正和江莉莉（2011, 2012）「動機—精神力場—行為假說」之心理決策流程存在的實質性，並利用Ng（1996）提出之「最小可感知的增量」作為苦樂感受的單位計數。根據實驗結果歸納以下主要結論：(1)個體的苦樂感受顯著存在本能性、社會性與大我世界（we-world）等主要快樂動機；(2)多元動機間的趨向衝突（approach-approach conflict）引導最適行為的調整；(3)快樂動機透過驅使決策的改變，亦使得對應不同決策結果產生的快樂感受呈現顯著的差異；以及(4)在凸顯大我世界動機後，個體的快樂感受顯著高於未凸顯前之情況。 According to Utilitarianism, happiness is the ultimate goal for human beings. The desire of a happy life drives people’s behavior toward the pursuit of happiness. Based on the theoretical framework of happiness proposed by Yu and Jiang (2012), this paper undertakes a series of experiments which investigate the determinants of money payoff to test the hypotheses of motivation-mental force-behavior, as well as the levels of happiness associated with behavioral decisions. The main results include: (1) The motivations of life instincts,social conformity and we-world are the main driving forces in deciding the al- location between money payoff and donation. (2) The approach-approach conflicts among various motivations lead individuals to adjust behavior optimally.(3) In each extensional situation, an individual’s anticipated degree of happiness, measured in term of “just perceivable units” (Ng, 1996), from the updated decision is significantly different from the levels attained in the previous stages.(4) Once an individual’s we-world motivation is evoked, the decision of the allocation between money payoff and donation brings forth higher degree of happiness which is never anticipated before.