An amusement writing instrument with a mechanical toy consists of an elongated pen body having a seat mounted on an end, a toy housing said seat and a working piece passing through said seat. The working piece comprises of a rod, pluralities of driving elements driven by the rod and pluralities of resilient devices for providing reciprocal movement. The ornament composes of a frontal and rear casings and a decorating object is further attached to the seat. The working piece is driven as the user propels the cartridge to disengage the frontal casings from the rear casing, creating a slit for allowing the decorating object to be extended and exposed.