Abstract: A writing instrument with a retractable refill mechanism comprises: an replaceable refill having a front end as the pen tip, a pen barrel which has a front end opening and accommodates said refill, a slider positioned at the rear end of the refill and slidable in the cavity inside of said pen barrel, a connecting rod with one end pivotally connected to said slider, an inner gear mounted inside of the pen barrel and off-axially and pivotally connected with said connecting rod, and an outer gear mounted inside of the pen barrel and engageable with said inner gear. Therefore, by means of the connecting rod off-axially connected to the rotatable inner gear, the rotation of the inner gear is converted to a linear motion of the slider.