When financing constraints exist and the adjustment costs associated with investment are high, firms will seek to lower long-term costs by maintaining stable investment through the smoothing of fixed asset investment using working capital. That is, when financing constraints exist, a firm's working capital investment will compete with fixed asset investment within a limited pool of available funds, resulting in a negative correlation with fixed asset investment. Therefore, by introducing the concept of "adjustment costs," it becomes possible to test for the existence of financing constraints. This paper also adds sales promotion investment as an additional subject of analysis, considering that adjustment costs vary according to asset characteristics, and sales promotion investment has lower adjustment costs compared to fixed asset investment. Because adjustment costs for sales promotion investment are lower, the investment smoothing effect using working capital is expected to be lower than that for fixed asset investment. Furthermore, this study conducts an empirical analysis of the bunching effect, which posits that when adjustment costs are high, firms tend to intermittently raise external funds—which carry high financing costs—store them in the form of working capital, and use them when making investment expenditures. The results demonstrate that financing constraint effects can be more clearly explained when the concept of "adjustment costs" incurred in corporate investment is employed. Specifically, the findings show that financing constraints exist in the fixed asset investment of domestically listed manufacturing firms, and that the investment smoothing effect through working capital must be taken into account in order to accurately identify the financing constraint effect.