A fixing device, comprising: a frame; a heating roller provided to the frame to produce heat, the heating roller having a roller rotation axis and a cylindrical surface; a press roller pressed against the cylindrical surface to feed a recording medium together with the heating roller along a feeding path; a peeler provided to the frame and having a peeling surface having a leading edge, the leading edge facing the cylindrical surface to peel off the recording medium on the cylindrical surface, the peeling surface facing the feeding path; a guide member positioned facing the peeling surface to guide the recording medium which has passed through between the heating roller and the press roller to downstream of the feeding path, the guide member being movable between a near position and a far position, the near position being closer to the peeling surface than the far position; a first bias unit that biases the guide member to the near position; and a detection member on a downstream side with respect to the heating roller in the feeding path, the detection member being displaceable when contacting with the recording medium; characterized by a rotation member supported to the frame and having a rotation axis and a circumferential edge, the rotation axis being parallel to the roller rotation axis, the rotation member being positioned in a manner that a part of the circumferential edge protrudes from the peeling surface to the guiding member in a virtual plane perpendicular to the rotation axis, an optical sensor fixed to the frame, and having a light emitter for emitting a light beam and a light receiver for receiving the light beam traveling from the light emitter to the light receiver, the optical sensor generating an output signal; a blocking member that interlocks with the detection member, the detection member being movably supported by the guide member as to be pivotable between a falling position and a standing position about a pivotal shaft, and the blocking member blocking the light beam when the guide member is at the near position and no sheet is passing the detection member, and letting the light beam pass when the guide member is at the pass far position or a sheet is passing the detection member, the blocking member being adapted to switch between the light block and the light passage in accordance with the displacement of the detection member; and a controller configured to determine that a jam of the recording medium has occurred if the light receiver receives the light beam continuously for a predetermined time period. a frame; a heating roller provided to the frame to produce heat, the heating roller having a roller rotation axis and a cylindrical surface; a press roller pressed against the cylindrical surface to feed a recording medium together with the heating roller along a feeding path; a peeler provided to the frame and having a peeling surface having a leading edge, the leading edge facing the cylindrical surface to peel off the recording medium on the cylindrical surface, the peeling surface facing the feeding path; a guide member positioned facing the peeling surface to guide the recording medium which has passed through between the heating roller and the press roller to downstream of the feeding path, the guide member being movable between a near position and a far position, the near position being closer to the peeling surface than the far position; a first bias unit that biases the guide member to the near position; and a detection member on a downstream side with respect to the heating roller in the feeding path, the detection member being displaceable when contacting with the recording medium; characterized by a rotation member supported to the frame and having a rotation axis and a circumferential edge, the rotation axis being parallel to the roller rotation axis, the rotation member being positioned in a manner that a part of the circumferential edge protrudes from the peeling surface to the guiding member in a virtual plane perpendicular to the rotation axis, an optical sensor fixed to the frame, and having a light emitter for emitting a light beam and a light receiver for receiving the light beam traveling from the light emitter to the light receiver, the optical sensor generating an output signal; a blocking member that interlocks with the detection member, the detection member being movably supported by the guide member as to be pivotable between a falling position and a standing position about a pivotal shaft, and the blocking member blocking the light beam when the guide member is at the near position and no sheet is passing the detection member, and letting the light beam pass when the guide member is at the pass far position or a sheet is passing the detection member, the blocking member being adapted to switch between the light block and the light passage in accordance with the displacement of the detection member; and a controller configured to determine that a jam of the recording medium has occurred if the light receiver receives the light beam continuously for a predetermined time period.