A substrate processing apparatus includes a chamber having an inner space where a process is carried out with respect to a substrate and an exhaust unit for exhausting substance in the inner space to the outside. The exhaust unit includes a first exhaust plate located at an upstream of an exhaust path of the substance, the first exhaust plate having first exhaust holes, and a second exhaust plate located at a downstream of the exhaust path, the first exhaust plate having second exhaust holes. The first exhaust plate is disposed outside a support member, and the second exhaust plate is disposed below the first exhaust plate generally in parallel to the first exhaust plate. The exhaust unit further includes first covers for selectively opening and closing the first exhaust holes and second covers for selectively opening and closing the second exhaust holes.