Provided are a polygon mirror assembly and a scan device. A polygon mirror assembly includes: a polygon mirror including a plurality of reflection surfaces spaced apart from a rotation axis by a predetermined distance; a first motor for rotating the polygon mirror around the rotation axis; a second motor for moving the polygon mirror in a first axial direction such that the rotation axis is tilted while the first motor rotates the polygon mirror; and a clock signal extraction surface for extracting a clock signal for detecting a change in a rotational speed of the first motor.