According to one aspect of the present invention, a pattern inspection apparatus includes a first diaphragm that is positioned on an optical path of a reflection illumination optical system and has a first reference pattern of a line-and-space pattern formed thereon; a semi-transmission reflection plate configured to reflect a portion of a reference pattern image that has passed through the first reference pattern; a second diaphragm which is positioned on an optical path of the imaging optical system, on which the portion of the reference pattern image reflected by the semi-transmission reflection plate is projected, and which has a second reference pattern of a line-and-space pattern formed thereon; and a first time delay integration sensor (TDI sensor) configured to receive the portion of the reference pattern image that has passed through the second reference pattern.