Displacement detecting device and optical instrument having the same

A displacement detecting device, comprising:

• a light source configured to project light to an object to be examined, said light source being movable relative to the object to be examined;
• a first reflecting element being fixed to the object to be examined and including a reflection portion configured to reflect light from said light source and a non-reflection portion;
• a first light receiving element configured to receive light reflected by said first reflecting element;
• a second reflecting element being fixed to the object to be examined and including a reflection portion configured to reflect light from said light source and a non-reflection portion;
• a second light receiving element configured to receive light reflected by said second reflecting element;
• and
• a housing configured to accommodate and hold therein said light source, said first reflecting element, said first light receiving element, said second reflecting element and said second light receiving element, said housing having an inner wall including a portion which is configured so that, when light passed through the non-reflection portion of said first reflecting element is incident on said inner wall, said portion reduces light directed therefrom toward said second light receiving element.