Displacement detector

A displacement detector comprising:

• a scale having a diffraction grating;
• and a detection head, which is arranged being capable of relatively moving with respect to the scale, emitting interference light to the scale and receiving diffracted light sent from the scale,
• the detection head including:
• a light source emitting the interference light;
• a light dividing section for dividing light, which has been sent from the light source, into two beams of light;
• an optical element, which is arranged for each of the two beams of light sent from the light dividing section, for reflecting the beam of light sent from the light dividing section and making the beam of light be incident upon the scale as incident light;
• and
• a retroreflector, which is arranged for each of the beams of diffracted light generated when the two beams of light incident upon the scale are diffracted by the diffraction grating, for retroreflecting the diffracted light and making the light be incident upon the scale as retroreflected light,
• wherein the incident light and the retroreflected light are incident in a direction perpendicular to a diffraction grating groove, and an angle formed between the incident light and the normal line vector of the scale is larger than an angle formed between the retroreflected light and the normal line vector of the scale.