An absolute encoder comprising: a light-emitting mechanism including an emission surface that emits detection light; and a light-receiving mechanism including a scale plate having a scale area and a light-receiving area configured to receive the detection light emitted from the emission surface and passing through the scale area of the scale plate, wherein the light-receiving area is formed to linearly extend in a light-receiving axis direction (Dp), the scale plate has a disc-like shape, the light-emitting mechanism is positioned in an outer side than the scale area as viewed in a radial direction of the scale plate, and the light-receiving mechanism is positioned in an inner side than the scale area as viewed in the radial direction of the scale plate and is set to a position relationship in which the light-receiving axis direction (Dp) is a direction parallel to a chord of the disk-like shape of the scale plate, characterized in that the light-emitting mechanism and the light-receiving mechanism are set to a position relationship that inclines an irradiation axis (A r) extending from the emission surface through the scale area to the light-receiving area relative to a plane including the light-receiving axis direction (Dp) and being parallel to_a rotation axis direction (D a) of the scale plate, and the detection light which is emitted from an inner end position at the emission surface as viewed in the radial direction and which directs to an outer end position at the light-receiving area as viewed in the radial direction is formed as inner end detection light (Le), and reflection detection light in which the inner end detection light (Le) is reflected on the light-receiving area toward the scale plate is formed as outer end reflection detection light (Lre), the position relationship between the light-emitting mechanism and the light-receiving mechanism is set by setting an inner end incident angle (θ) of the inner end detection light relative to the plane including the light-receiving axis direction (Dp) and parallel to the rotation axis direction (Da) to prevent the outer end reflection detection light from being reflected again on the scale plate and reaching the light-receiving area. a light-emitting mechanism including an emission surface that emits detection light; and a light-receiving mechanism including a scale plate having a scale area and a light-receiving area configured to receive the detection light emitted from the emission surface and passing through the scale area of the scale plate, wherein the light-receiving area is formed to linearly extend in a light-receiving axis direction (Dp), the scale plate has a disc-like shape, the light-emitting mechanism is positioned in an outer side than the scale area as viewed in a radial direction of the scale plate, and the light-receiving mechanism is positioned in an inner side than the scale area as viewed in the radial direction of the scale plate and is set to a position relationship in which the light-receiving axis direction (Dp) is a direction parallel to a chord of the disk-like shape of the scale plate, characterized in that the light-emitting mechanism and the light-receiving mechanism are set to a position relationship that inclines an irradiation axis (A r) extending from the emission surface through the scale area to the light-receiving area relative to a plane including the light-receiving axis direction (Dp) and being parallel to_a rotation axis direction (D a) of the scale plate, and the detection light which is emitted from an inner end position at the emission surface as viewed in the radial direction and which directs to an outer end position at the light-receiving area as viewed in the radial direction is formed as inner end detection light (Le), and reflection detection light in which the inner end detection light (Le) is reflected on the light-receiving area toward the scale plate is formed as outer end reflection detection light (Lre), the position relationship between the light-emitting mechanism and the light-receiving mechanism is set by setting an inner end incident angle (θ) of the inner end detection light relative to the plane including the light-receiving axis direction (Dp) and parallel to the rotation axis direction (Da) to prevent the outer end reflection detection light from being reflected again on the scale plate and reaching the light-receiving area.