Directed energy deposition (DED), one of the additive manufacturing processes available for metals, is being employed in various industries. However, pore generation still remains a fatal problem that deteriorates the mechanical strength in DED products. In this study, analytical evaluation on pore generation in DED is conducted by introducing a special chamber. By classifying residual failures inside produced parts, pore generation is suppressed along with its cause. Experimental results show that the porosity rate can be drastically reduced in DED products by filling the chamber with argon, increasing the cooling rate, and applying re-melting process during deposition.