A stroller includes a main frame, a pedal, a front wheel frame, and a positioning device. The positioning device includes a lower cover, an upper cover, a rotation knob, and a locking rod. Thus, the front wheel frame is locked to and unlocked from the main frame by moving the drive plate of the rotation knob, so that the positioning device is operated easily and rapidly. In addition, when the positioning device is unlocked, a click sound is produced so as to notify the user that the positioning device is unlocked and the front wheel frame is rotatable relative to the main frame freely, thereby facilitating the user judging the state (locked or unlocked) of the front wheel frame.