Patent ID: 8425003

Claim:
A position detecting device for detecting a position of an object, comprising: a light emitting portion that emits light; a light receiving portion that receives the light from the light emitting portion; a scale that is arranged between the light emitting portion and the light receiving portion, and includes a position detecting pattern and a smear detecting pattern; and a control portion which determines position from the position detecting pattern and determines smear from the smear detecting pattern, wherein the position detecting pattern has a first light transmitting portion for transmitting the light from the light emitting portion and a first light interception portion for intercepting the light from the light emitting portion which are alternately arranged in a detection range of the object, wherein the smear detecting pattern for detecting smear of the scale has a second light transmitting portion for transmitting the light from the light emitting portion and a second light interception portion for intercepting the light from the light emitting portion which are alternately arranged, wherein the scale is a rotary scale having a circular plate shape, and wherein the smear detecting pattern is arranged at an inner diameter side of the rotary scale with respect to the position detecting pattern.