A displacement detection apparatus, comprising: a light source configured to emit light; a light flux dividing portion configured to divide light emitted from the light source into a first light flux and a second light flux; a first transmission-type diffraction grating configured to diffract the first light flux divided by the light flux dividing portion and reflected by a surface to be measured of a member to be measured, and cause the diffracted first light flux to enter again the surface to be measured of the member to be measured; a reflection portion configured to reflect the second light flux divided by the light flux dividing portion; a light flux coupling portion configured to couple the first light flux, which is caused to enter the surface to be measured of the member to be measured after being diffracted by the first diffraction grating and is reflected by the surface to be measured of the member to be measured, and the second light flux reflected by the reflection portion; a light receiving portion configured to receive interference light that is obtained by coupling the first light flux and the second light flux by the light flux coupling portion; a second transmission-type diffraction grating arranged on an optical path between the member to be measured and the light receiving portion of the first light flux, the second transmission-type diffraction grating being configured to diffract the first light flux, which is caused to enter the surface to be measured of the member to be measured after being diffracted by the first diffraction grating and is reflected by the surface to be measured of the member to be measured; and a relative positional information output portion configured to output displacement information in a height direction of the surface to be measured of the member to be measured, based on an intensity of the interference light received by the light receiving portion, wherein, when the surface to be measured is tilted, the optical path length of the first light flux will change, and the second transmission-type diffraction grating is provided to cancel the change of the optical path length. a light source configured to emit light; a light flux dividing portion configured to divide light emitted from the light source into a first light flux and a second light flux; a first transmission-type diffraction grating configured to diffract the first light flux divided by the light flux dividing portion and reflected by a surface to be measured of a member to be measured, and cause the diffracted first light flux to enter again the surface to be measured of the member to be measured; a reflection portion configured to reflect the second light flux divided by the light flux dividing portion; a light flux coupling portion configured to couple the first light flux, which is caused to enter the surface to be measured of the member to be measured after being diffracted by the first diffraction grating and is reflected by the surface to be measured of the member to be measured, and the second light flux reflected by the reflection portion; a light receiving portion configured to receive interference light that is obtained by coupling the first light flux and the second light flux by the light flux coupling portion; a second transmission-type diffraction grating arranged on an optical path between the member to be measured and the light receiving portion of the first light flux, the second transmission-type diffraction grating being configured to diffract the first light flux, which is caused to enter the surface to be measured of the member to be measured after being diffracted by the first diffraction grating and is reflected by the surface to be measured of the member to be measured; and a relative positional information output portion configured to output displacement information in a height direction of the surface to be measured of the member to be measured, based on an intensity of the interference light received by the light receiving portion, wherein, when the surface to be measured is tilted, the optical path length of the first light flux will change, and the second transmission-type diffraction grating is provided to cancel the change of the optical path length.