An apparatus for monitoring an interior of a process chamber including a process chamber including a chamber body and a view port defined in the chamber body, a cover section including a pinhole in one end, the cover section disposed to correspond to an end portion of the view port, the cover section having a first length in a direction toward a center point of the process chamber, and a sensing unit inserted into the view port to monitor the interior of the process chamber through the pinhole, a region in the process chamber to be sensed by the sensing unit determined based on the first length may be provided.