According to one embodiment, a pattern inspection apparatus includes a light source, a beam splitter, a first optical system, a second optical system, a controller, a phase controller and a detector. The beam splitter splits an emitted light into first and second optical paths. The first optical system delivers the light to a first pattern and delivers a first reflected light from the first pattern. The second optical system delivers the light to a second pattern and delivers a second reflected light from the second pattern. The controller is provided on the optical path, and intensities of the first and second reflected lights are substantially equal. The phase controller is provided on the optical path, and phases of the first and second reflected lights are inverted. In addition, the detector detects a light that the first and second reflected lights are made to interfere with each other.