A stylus pen may be optimized to a housing having a specific shape and may improve a magnitude of a pen signal. A ferrite core is mounted in a stylus pen and has a through-hole formed along a longitudinal direction of the stylus pen. The ferrite core has a first cross-sectional shape in a first vertical direction perpendicular to the longitudinal direction and a second cross-sectional shape in a second vertical direction perpendicular to both the longitudinal direction and the first vertical direction, the first cross-sectional shape is different from the second cross-sectional shape, the ferrite core includes a curved portion disposed at one end of the ferrite core, and the curved portion includes at least two curved surfaces that are curved from one side surface of one end of the ferrite core to a portion adjacent to the through-hole of the ferrite core in a direction toward the through-hole.