A displacement measuring apparatus includes a light source configured to illuminate light, and a photodetector provided on a structure and configured to detect reflected light from a reflection portion of a scale that alternately and periodically includes a convex portion scattering the light from the light source and the reflection portion reflecting the light, the displacement measuring apparatus measures a relative displacement between the structure and the photodetector based on a detection result from the photodetector, a length of the reflection portion in a period direction of the scale is greater than a half of a sum of lengths of the convex portion and the reflection portion, and the reflection portion includes a curved concave portion that reflects and collects the light illuminated from the light source.