Income smoothing is an act of accounting engineering by exploiting gaps in accounting standards. This study aims to determine the motives for income-shifting management. Based on agency theory, this study tested three hypotheses on two income-smoothing objects: operating income and net income. This research is a quantitative study with data in Indonesian public manufacturing companies’ financial statements dated December 31, 2009 - 2018 obtained from the Indonesian Capital Market Directory. Hypothesis testing uses a binary logistic regression approach. The practice of income smoothing exists in manufacturing companies in Indonesia. Management shift income with object engineering is gross profit by 30.2% and net income by 21.7%. Hypothesis testing confirms that the commissionaire board size is not a mechanism of supervision effectiveness. The independent commissioners’ size was able to suppress income smoothing in manufacturing companies. Audit tenure has a negative effect on income smoothing. The audit period is directly proportional to the auditor’s ability to limit income smoothing. These results contribute to the formulation of policies, especially in improving the quality of corporate governance. Even the public and investors can understand the indications of income smoothing practices. New evidence suggests that income smoothing is less likely to be desired by corporate governance mechanisms. The motive for income smoothing is considered opportunistic. Audit tenure improves the quality of oversight of accounting engineering actions, contrary to the previous opinion that tenure reduces auditor independence.