本研究主要係探討審計委員會及其設置動機對於盈餘管理行為之長期影響。此外，本研究亦針對審計委員會運作品質，探討各類運作品質是否因設置年數或設置動機而改變對於盈餘管理之影響。
本研究採用我國2004年至2019年排除金融業之上市櫃公司為全部樣本，於假說一檢視設置審計委員會與否對於盈餘管理之影響，結果顯示有設置審計委員會之公司相較於無設置者，更能抑制盈餘管理，此結果與先前研究結果一致(Dechow et al.，1996；McMullen，1996；許文馨，2014)。接著於假說二分別針對有設置審計委員會之樣本及設置審計委員會以後之樣本，檢視審計委員會設置年數對於盈餘管理之影響。結果顯示，設置審計委員會以後相較於設置前更能抑制盈餘管理，且隨著設置年數增加，相較於設置前期更能抑制盈餘管理，顯示審計委員會隨著設置時間越長，將持續增進監管效益。然而於假說三，本研究發現僅有自願設置審計委員會之公司會隨著設置年數增加持續強化抑制盈餘管理之能力，相較之下，強制設置審計委員會之公司則無持續進步之效果。於假說四亦發現自願設置審計委員會之公司，相較於強制設置者，更能夠透過提升部分運作品質以增進監管效力。
本研究透過檢視審計委員會設置動機差異對於盈餘管理之長期影響趨勢，發現自願設置之審計委員會能夠隨著設置年數增加持續增進監管能力，相較於強制設置之審計委員會更有能力持續強化公司治理效益，亦更符合金管會之期許，因此本研究建議金管會應以鼓勵自願設置之方式推動審計委員會制度。

The primary purpose of this study is to inspect the long-term effects of audit committee’s forming motivation on earnings management. Moreover, this study also investigates the association between the audit committee’s operating quality and earnings quality, taking the forming year and forming motivation into consideration.
This study first examines the effects of the audit committee’s establishment on earnings management, using the sample of all the listed companies in the Taiwan Stock Exchange (TWSE) in the period of 2004-2019. The result shows that audit committees can reduce earnings management, which is consistent with prior research (Dechow et al., 1996; McMullen, 1996; Hsu, 2014). This study also considers the effect of forming year, and the result shows that audit committees will keep strengthening the skill of reducing earnings management as time goes on. While including the effect of the forming motivation, this study discovers that the contribution of improvement only lies in the category of voluntary formation. In the mandatory formation category, however, audit committees do not have the ability to keep improving their monitoring skill. This study also observes that audit committees in voluntary formation, compared with those in mandatory formation, restrain earnings management by increasing the operating quality of the audit committee.
Overall, the results suggest that voluntary formation performs better at enhancing corporate governance in the long-term period. As a result, this study suggests that FSC should promote the audit committee system through voluntary formation instead of mandatory formation.

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