Position sensor assemblies having compact structures and capable of precisely sensing a position change, and optical devices including the same are disclosed. A position sensor assembly is provided that includes: a sensing unit that outputs a signal varying as a magnetic force varies; and a magnet spaced apart from the sensing unit and i movably disposed with respect to the sensing unit, and comprising protrusion units of opposite polarities that protrude from each end portion of the magnet in one surface of the magnet toward the sensing unit.