Displacement measuring apparatus

A displacement measuring apparatus, comprising:

• a first light detector including a first emitter that illuminates optically identifiable marks disposed on a moving body, and a first light receiver that detects light from the optically identifiable marks;
• a second light detector including a second emitter that illuminates the optically identifiable marks and a second light receiver that detects light from the optically identifiable marks, wherein the second light detector is arranged at a predetermined interval from the first light detector in a moving direction of the moving body;
• an identical point detecting unit that determines a first time at which the first light detector detects a first mark among the optically identifiable marks, and a second time different from the first time at which the second light detector detects the first mark;
• a velocity calculating unit that calculates a moving velocity of the moving body by using the first time and the second time determined by the identical point detecting unit;
• and
• a time-sharing light emitting unit that allows the first emitter and the second emitter to emit light in a time-sharing manner.