The present application relates to a slot die coating apparatus and, more particularly, to a slot die coating apparatus which can ensure the coating stability of a substrate film by reducing pressure oscillations within a vacuum chamber when slot die coating is carried out. The slot die coating apparatus according to the present application can effectively dampen pressure oscillations within a vacuum chamber by connecting a pressure oscillation reducing tank to the vacuum chamber and thus can ensure the coating stability of a substrate film, resulting in a reduction in the proportion of defective products.