1958年Modigliani and Miller在完美市場的假設下得到了資本結構無關的結果。但現實社會不存在完美市場，故企業投資需向外融資時，會因代理問題、資訊不對稱而需負擔較高的融資成本。Fazzari et al(1988)認為這會對不同內部資金廠商的投資行為造成不同程度的影響。更進一步說，融資受限廠商投資對現金流量的敏感度較大。後續有相當多的研究，但大多忽略了營運資金的角色。 企業投資需向外融資時是因內部資金不足，而內部資金不僅限於現金流量。Fazzari and Petersen(1993)認為營運資金具緩衝內部資金不足之效，也就是說在考量企業投資行為與內部資金多寡之關係時，除現金流量外，營運資金亦因考量在內。考量營運資金還有一個好處：可以釐清文獻上爭論已久的一項議題：現金流量究竟為投資機會抑或是內部資金的代理變數。 本研究以台灣上市櫃製造業公司為標的，希望能就上述議題提供一些實證資料以為後續研究參考。實證結果簡述如下：(1)當營運資金作為固定投資模型的內生變數時，其估計係數應為負。(2)證實應用傳統模進行分析可能造成現金流量對固定投資的影響被低估。 Modigliani and Miller (1958) shows, under the perfect markets assumptions, capital structures are irrelevant. In reality, there is no perfect market but agency costs and information asymmetric costs. Therefore firms have to pay higher financing costs when external funds are needed. Fazzari, Hubbard, and Petersen (1988) argue this shall have impacts over firm’s investment behaviors. Moreover, more financial constrained more seriously impacts. Many follow-up studies but the roles of working capital are often neglected. In general, researches of this regard treat cash flow as the only internal funds. However, internal funds are not limited to cash flows only. Fazzri and Petersen (1993) argue that working capital provides a cushion while lacking of internal funds. In addition, taking into consideration the role of working capital in firms’ investment also helps to clarify a long been discussed issue—whether cash flow is a proxy for financial constraint or it represents the investment opportunities given the marginal Tobin’s Q is not available in reality. Not many works on Taiwan manufacturing firms’ investment behaviors while facing financial constraints can be found in literature. Therefore the main purpose of this study is to provide related empirical evidences. In short, empirical findings are pretty much similar to that of U.S. and China. The empirical predictions in this article are summarized as follows: ( 1 )When working capital investment as an endogenous variable is included in a fixed-investment regression, its estimated coefficient will be negative. ( 2 ) Analyzing using the standard “within-firm” estimator will underestimates the impact of cash-flow shocks on fixed investments.