Abstract: A stroller comprises a seat, a fork-type handlebar interchangeable between a forward and a backward positions with respect to the seat, four wheel sets divided into two pairs, each pair consisting of a front and a rear wheel sets at respective lateral side of the seat, with related support tubes provided therein an extending wire, connecting to respective twin lock pins at opposite ends in cooperation with associated twin lock holes formed around respective vertical spindle of the wheel sets, and a pair of actuators on the support tubes at opposite sides of the seat. The front wheel sets are swivel freely while the rear wheel sets can only move fore and aft in a predetermined orientation when the handlebar is at the forward position, and vice versa when the handlebar is at the backward position.